@article {868, title = {A Large-Scale Empirical Study of LLM Orchestration and Ensemble Strategies for Sentiment Analysis in Recommender Systems}, journal = {Future Internet}, volume = {18}, year = {2026}, pages = {112}, abstract = {

This paper presents a comprehensive empirical evaluation comparing meta-model aggregation strategies with traditional ensemble methods and standalone models for sentiment analysis in recommender systems beyond standalone large language model (LLM) performance. We investigate whether aggregating multiple LLMs through a reasoning-based meta-model provides measurable performance advantages over individual models and standard statistical aggregation approaches in zero-shot sentiment classification. Using a balanced dataset of 5000 verified Amazon purchase reviews (1000 reviews per rating category from 1 to 5 stars, sampled via two-stage stratified sampling across five product categories), we evaluate 12 different leading pre-trained LLMs from four major providers (OpenAI, Anthropic, Google, and DeepSeek) in both standalone and meta-model configurations. Our experimental design systematically compares individual model performance against GPT-based meta-model aggregation and traditional ensemble baselines (majority voting, mean aggregation). Results show statistically significant improvements (McNemar{\textquoteright}s test, p \< 0.001): the GPT-5 meta-model achieves 71.40\% accuracy (10.15 percentage point improvement over the 61.25\% individual model average), while the GPT-5 mini meta-model reaches 70.32\% (9.07 percentage point improvement). These observed improvements surpass traditional ensemble methods (majority voting: 62.64\%; mean aggregation: 62.96\%), suggesting potential value in meta-model aggregation for sentiment analysis tasks. Our analysis reveals empirical patterns including neutral sentiment classification challenges (3-star ratings show 64.83\% failure rates across models), model influence hierarchies, and cost-accuracy trade-offs ($130.45 aggregation cost vs. $0.24{\textendash}$43.97 for individual models per 5000 predictions). This work provides evidence-based insights into the comparative effectiveness of LLM aggregation strategies in recommender systems, demonstrating that meta-model aggregation with natural language reasoning capabilities achieves measurable performance gains beyond statistical aggregation alone.

}, keywords = {empirical evaluation, ensemble learning, large language models, LLM orchestration, meta-model aggregation, multi-model aggregation, reasoning models, Recommender Systems, sentiment classification, zero-shot sentiment analysis}, issn = {1999-5903}, doi = {https://doi.org/10.3390/fi18020112}, url = {https://www.mdpi.com/1999-5903/18/2/112}, author = {Roumeliotis, Konstantinos I. and Margaris, Dionisis and Spiliotopoulos, Dimitris and Vassilakis, Costas} } @article {869, title = {Optimizing Collaborative Filtering for Accurate Rating Predictions in Very Sparse Datasets}, journal = {Future Internet}, volume = {18}, year = {2026}, pages = {114}, abstract = {

Collaborative filtering is one of the most widely used methods for user rating prediction in recommender systems. To evaluate a collaborative filtering system, rating datasets are typically used, which comprise thousands to millions of records consisting of user{\textendash}item{\textendash}rating tuples. Initially, a similarity metric is used to quantify the closeness between each user and every other user in the dataset, typically based on the ratings that each pair of users has given to the same items. Subsequently, the K users having the largest similarity to the target user are used to produce rating predictions, which lead to recommendations. A particularly challenging case arises when the rating dataset is very sparse. In this scenario, it is difficult not only to find users with commonly rated items but also to determine the optimal similarity metric and suitable values for variable K. Setting a small value for K results in extremely low prediction coverage, leading to unsuccessful recommendations, while setting a very large K value increases memory requirements and prediction/recommendation generation time. Through a multiparameter experiment, this work aims to determine the optimal settings for rating predictions when very sparse datasets are used in collaborative filtering recommender systems.

}, keywords = {collaborative filtering, K-nearest neighbors (KNN), optimal prediction settings, prediction accuracy, Rating prediction, Recommender Systems, similarity metrics, sparse collaborative filtering, Sparse Datasets}, issn = {1999-5903}, doi = {10.3390/fi18020114}, url = {https://www.mdpi.com/1999-5903/18/2/114}, author = {Lapadaki, Sofia-Anna and Nanos, John and Margaris, Dionisis and Vassilakis, Costas and Spiliotopoulos, Dimitris} } @article {844, title = {AI and Related Technologies in the Fields of Smart Agriculture: A Review}, journal = {Information}, volume = {16}, year = {2025}, pages = {100}, abstract = {

The integration of cutting-edge technologies{\textemdash}such as the Internet of Things (IoT), artificial intelligence (AI), machine learning (ML), and various emerging technologies{\textemdash}is revolutionizing agricultural practices, enhancing productivity, sustainability, and efficiency. The objective of this study is to review the literature regarding the development and evolution of AI as well as other emerging technologies in the various fields of Agriculture as they are developed and transformed by integrating the above technologies. The areas examined in this study are open field smart farming, vertical and indoor farming, zero waste agriculture, precision livestock farming, smart greenhouses, and regenerative agriculture. This paper links current research, technological innovations, and case studies to present a comprehensive review of these emerging technologies being developed in the context of smart agriculture, for the benefit of farmers and consumers in general. By exploring practical applications and future perspectives, this work aims to provide valuable insights to address global food security challenges, minimize environmental impacts, and support sustainable development goals through the application of new technologies.

}, keywords = {AI, artificial intelligence, indoor farming, IoT, precision agriculture, precision livestock, regenerative agriculture, smart farming, smart green, vertical farming, zero-waste agriculture}, issn = {2078-2489}, doi = {https://doi.org/10.3390/info16020100}, author = {Assimakopoulos, Fotis and Costas Vassilakis and Dionisis Margaris and Kotis, Konstantinos and Spiliotopoulos, Dimitris} } @article {861, title = {Automated Test Generation and Marking Using LLMs}, journal = {Electronics}, volume = {14}, year = {2025}, pages = {2835}, abstract = {

This paper presents an innovative exam-creation and grading system powered by advanced natural language processing and local large language models. The system automatically generates clear, grammatically accurate questions from both short passages and longer documents across different languages, supports multiple formats and difficulty levels, and ensures semantic diversity while minimizing redundancy, thus maximizing the percentage of the material that is covered in the generated exam paper. For grading, it employs a semantic-similarity model to evaluate essays and open-ended responses, awards partial credit, and mitigates bias from phrasing or syntax via named entity recognition. A major advantage of the proposed approach is its ability to run entirely on standard personal computers, without specialized artificial intelligence hardware, promoting privacy and exam security while maintaining low operational and maintenance costs. Moreover, its modular architecture allows the seamless swapping of models with minimal intervention, ensuring adaptability and the easy integration of future improvements. A requirements{\textendash}compliance evaluation, combined with established performance metrics, was used to review and compare two popular multilingual LLMs and monolingual alternatives, demonstrating the system{\textquoteright}s effectiveness and flexibility. The experimental results show that the system achieves a grading accuracy within a 17\% normalized error margin compared to that of human experts, with generated questions reaching up to 89.5\% semantic similarity to source content. The full exam generation and grading pipeline runs efficiently on consumer-grade hardware, with average inference times under 30 s.

}, keywords = {artificial intelligence, DeepSeek, exams, large language models, Llama, named entity recognition, Natural language processing, question{\textendash}answer generation, retrieval-augmented generation, Semantic Similarity, test generation, test marking}, issn = {2079-9292}, doi = {https://doi.org/10.3390/electronics14142835}, author = {Papachristou, Ioannis and Dimitroulakos, Grigoris and Vassilakis, Costas} } @article {849, title = {Brain Computer Interfaces: A literature review}, journal = {Hellenic Journal of Nursing}, volume = {TBD}, year = {2025}, abstract = {

Introduction: Brain Computer Interfaces (BCI) have significantly improved the quality of life of patients who use such technologies, restoring their health problems, such as hearing loss, vision, motor difficulties. Purpose: The purpose of this literature review was to describe recent developments in the field of BCI systems and related work that has been implemented in the last two decades. Methodology: A literature search of scientific articles of the last twenty years was carried out in the electronic databases PubMed and Scopus. The following keywords were used: brain-computer interface, BCI systems, privacy, neuroethics as well as synonyms and combinations of the terms. Results: The research field of BCI systems is a relatively new interdisciplinary field that integrates research groups from neuroscience, physiology, psychology, engineering, computer science, rehabilitation and other technical and health disciplines. Conclusions: The current trend of BCI systems is to enable new innovative communication paradigms, such as communication between human brains and communication between human brains and the Internet. Despite the benefits brought by this technological progress, it also creates opportunities for malicious actors to attack these systems, resulting in the threat of personal information of users as well as their physical integrity, but also affecting all activities that are directly or indirectly guided by BCI systems.

}, keywords = {BCI systems, Brain-Computer Interfaces, Neuroethics, privacy}, author = {Stathoulis, John D. and Bakalis, Vissarion I. and Costas Vassilakis} } @article {853, title = {Cost-Efficient RSSI-Based Indoor Proximity Positioning, for Large/Complex Museum Exhibition Spaces}, journal = {Sensors}, volume = {25}, year = {2025}, pages = {2713}, abstract = {

RSSI-based proximity positioning is a well-established technique for indoor localization, featuring simplicity and cost-effectiveness, requiring low-price and off-the-shelf hardware. However, it suffers from low accuracy (in NLOS traffic), noise, and multipath fading issues. In large complex spaces, such as museums, where heavy visitor traffic is expected to seriously impact the ability to maintain LOS, RSSI coupled with Bluetooth Low Energy (BLE) seems ideal in terms of market availability, cost-/energy-efficiency and scalability that affect competing technologies, provided it achieves adequate accuracy. Our work reports and discusses findings of a BLE/RSSI-based pilot, implemented at the Museum of Modern Greek Culture in Athens, involving eight buildings with 47 halls with diverse areas, shapes, and showcase layouts. Wearable visitor BLE beacons provided cell-level location determined by a prototype tool (VTT), integrating in its architecture different functionalities: raw RSSI data smoothing with Kalman filters, hybrid positioning provision, temporal methods for visitor cell prediction, spatial filtering, and prediction based on popular machine learning classifiers. Visitor movement modeling, based on critical parameters influencing signal measurements, provided scenarios mapped to popular behavioral models. One such model, {\textquotedblleft}ant{\textquotedblright}, corresponding to relatively slow nomadic cell roaming, was selected for basic experimentation. Pilot implementation decisions and methods adopted at all layers of the VTT architecture followed the overall concept of simplicity, availability, and cost-efficiency, providing a maximum infrastructure cost of 8 Euro per m2 covered. A total 15 methods/algorithms were evaluated against prediction accuracy across 20 RSSI datasets, incorporating diverse hall cell allocations and visitor movement patterns. RSSI data, temporal and spatial management with simple low-processing methods adopted, achieved a maximum prediction accuracy average of 81.53\% across all datasets, while ML algorithms (Random Forest) achieved a maximum prediction accuracy average of 87.24\%.

}, keywords = {Bluetooth Low Energy, indoor proximity positioning, large/complex museums, machine learning classification, museum visitor modeling, RSSI temporal/spatial methods}, issn = {1424-8220}, doi = {https://doi.org/10.3390/s25092713}, url = {https://doi.org/10.3390/s25092713}, author = {Philippopoulos, Panos I. and Koutrakis, Kostas N. and Tsafaras, Efstathios D. and Papadopoulou, Evangelia G. and Sigalas, Dimitrios and Tselikas, Nikolaos D. and Ougiaroglou, Stefanos and Costas Vassilakis} } @article {867, title = {Decorated papers in bookbinding: A proposal for the creation of metadata for its documentation.}, journal = {Journal of Integrated Information Management}, volume = {10}, year = {2025}, abstract = {

Purpose: The purpose of this study is the formulation of a metadata schema that represents the structure, methods, materials and designs of 19th century bookbindings. The creation of a metadata schema contributes in systematizing the information collected regarding bookbinding, guides and organizes the information collection and management process, and facilitates search and retrieval. For each individual element of the binding process, the corresponding metadata are defined. The proposed metadata schema focuses on the representation of decorated papers used in books as covers, or parts of covers, and as endpapers. Mapping of metadata elements to Dublin Core elements is also provided, to facilitate standardization and interoperability.

Methodology: To achieve systematic documentation of the decorated papers and define a comprehensive and complete set of metadata, the first step was to categorize them and identify their properties. Initially, the techniques, materials, types of designs, colours, and characteristics of the papers were studied. To this end, information from similar categorizations was sourced from the literature and the internet and utilized. Best practices followed by international standards for defining metadata and types of information encoding using controlled vocabularies and rules were identified and adopted.

Findings: This study presents a set of comprehensive and organized metadata elements for decorated papers, which can be used for the study and documentation of decorated papers.

Value: Today, in Greece, there have been only a few sporadic references to decorated papers, however no organized recording or systematic classification of these papers and their attributes is available. The present study constitutes the first step towards creating a metadata schema that will enable the recording, organization, management, and utilization of decorated paper information, as well as a populated database, aiming to deepen the understanding of book collection, correlate it with the spatial-temporal context of its use, and promote and disseminate the material to user communities.

}, keywords = {coloured paper, decorated paper, embossed paper, marble paper, Metadata, paste paper, printed paper, sprinkled paper, surface paper}, doi = {10.26265/JIIM.V10I2.41054}, url = {https://ejournals.epublishing.ekt.gr/index.php/jiim/article/view/41054/31947}, author = {Ntalouka, Efthalia and Kyriaki-Manesis, Daphne and Choulis, Konstantinos and Vassilakis, Costas} } @article {860, title = {An evaluation review of user similarity metrics in sparse collaborative filtering datasets}, journal = {International Journal of Data Science and Analytics}, year = {2025}, abstract = {

Collaborative filtering (CF) is one of the most prominent recommender system (RecSys) techniques of the recent years. CF generates rating predictions for the items that the user has not evaluated yet, using the evaluations of users with similar likings to the same items. Therefore, in CF the task of finding these users (which can be considered as reliable recommenders) is of high importance, while this task is especially challenging on sparse datasets. To this end, many user similarity metrics have been introduced and used in the literature, such as the Vector (or Cosine) Similarity metric, the Spearman rank correlation, the Pearson Correlation Coefficient (PCC), and others. For a CF RecSys, the use of the most efficient similarity metric is of great importance. This paper assesses the effectiveness of 15 user similarity metrics in sparse CF datasets, by conducting an extensive set of experiments. These experiments include 10 sparse CF datasets with diverse item domains, two neighbour selection approaches, two rating prediction formulas, and three rating prediction accuracy metrics. The evaluation results show that the metrics that achieve the best prediction results are found to be the Spearman rank correlation, followed by the Adjusted Rand Index, the Constrained PCC, and the Chebysev distance. Interestingly, the most widely used similarity metrics in CF research, i.e. the PCC and the Cosine Similarity, are not among the best performing metrics.

}, keywords = {collaborative filtering, Evaluation review, Recommender Systems, Sparse Datasets, User similarity metrics}, issn = {2364-4168}, doi = {10.1007/s41060-025-00846-4}, author = {Sgardelis, Kiriakos and Margaris, Dionisis and Spiliotopoulos, Dimitris and Vassilakis, Costas} } @booklet {846, title = {Experimental results for Evaluating User Similarity Metrics in Sparse Collaborative Filtering Datasets (version 2)}, year = {2025}, abstract = {

In this technical report, we present the experimental findings from evaluating 15 user similarity metrics when applied in sparse collaborative filtering (CF) datasets.

}, keywords = {collaborative filtering, Evaluation, Sparse Datasets, User similarity metrics}, url = {https://soda.dit.uop.gr/sites/soda.dit.uop.gr/files/publications/technical-reports/soda-TR-24001-v2.pdf}, author = {Kiriakos Sgardelis and Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @article {847, title = {Fine-Tuning Large Language Models for Ontology Engineering: A Comparative Analysis of GPT-4 and Mistral}, journal = {Applied Sciences}, volume = {15}, year = {2025}, month = {February}, pages = {2146}, abstract = {

Ontology engineering (OE) plays a critical role in modeling and managing structured knowledge across various domains. This study examines the performance of fine-tuned large language models (LLMs), specifically GPT-4 and Mistral 7B, in efficiently automating OE tasks. Foundational OE textbooks are used as the basis for dataset creation and for feeding the LLMs. The methodology involved segmenting texts into manageable chapters, generating question{\textendash}answer pairs, and translating visual elements into description logic to curate fine-tuned datasets in JSONL format. This research aims to enhance the models{\textquoteright} abilities to generate domain-specific ontologies, with hypotheses asserting that fine-tuned LLMs would outperform base models, and that domain-specific datasets would significantly improve their performance. Comparative experiments revealed that GPT-4 demonstrated superior accuracy and adherence to ontology syntax, albeit with higher computational costs. Conversely, Mistral 7B excelled in speed and cost efficiency but struggled with domain-specific tasks, often generating outputs that lacked syntactical precision and relevance. The presented results highlight the necessity of integrating domain-specific datasets to improve contextual understanding and practical utility in specialized applications, such as Search and Rescue (SAR) missions in wildfire incidents. Both models, despite their limitations, exhibited potential in understanding OE principles. However, their performance underscored the importance of aligning training data with domain-specific knowledge to emulate human expertise effectively. This study, based on and extending our previous work on the topic, concludes that fine-tuned LLMs with targeted datasets enhance their utility in OE, offering insights into improving future models for domain-specific applications. The findings advocate further exploration of hybrid solutions to balance accuracy and efficiency.

}, keywords = {domain-specific knowledge, large language models fine-tuning, ontology engineering, search and rescue}, issn = {2076-3417}, doi = {https://doi.org/10.3390/app15042146}, author = {Doumanas, Dimitrios and Soularidis, Andreas and Spiliotopoulos, Dimitris and Costas Vassilakis and Kotis, Konstantinos} } @article {852, title = {From Rating Predictions to Reliable Recommendations in Collaborative Filtering: The Concept of Recommendation Reliability Classes}, journal = {Big Data and Cognitive Computing}, volume = {9}, year = {2025}, pages = {106}, abstract = {

Recommender systems aspire to provide users with recommendations that have a high probability to be accepted. This is accomplished by producing rating predictions for products that they have not evaluated and afterwards, the products having the highest prediction scores are recommended to them. Collaborative filtering is a popular recommender system technique which generates rating prediction scores by blending the ratings that users with similar likings have previously set to these products. However, predictions may entail errors, which will either lead to recommending products that the users would not accept or failing to recommend products that the users would really accept. The first case is considered much more critical, since the recommender system will significantly lose reliability and consequently interest. In this paper, after performing a study on rating prediction confidence factors in collaborative filtering (a) we introduce the concept of prediction reliability classes, (b) we rank these classes in relation to the utility of the rating predictions belonging to each class and (c) we present a collaborative filtering recommendation algorithm which exploits these reliability classes for prediction formulation. The efficacy of the presented algorithm is evaluated through an extensive multi-parameter evaluation process, which demonstrates that it significantly enhances recommendation quality.

}, keywords = {collaborative filtering, Evaluation, Rating Predictions, Recommender Systems, reliability classes, reliable recommendations}, issn = {2504-2289}, doi = {10.3390/bdcc9040106}, author = {Dionisis Margaris and Costas Vassilakis and Spiliotopoulos, Dimitris} } @article {843, title = {A generalized, rule-based method for the detection of intermittent faults in software programs}, journal = {Journal of Systems and Software}, volume = {219}, year = {2025}, pages = {112228}, abstract = {

Intermittent faults are a very common problem in the software world, and are very hard to locate and correct, due to the fact that they manifest their presence only under certain circumstances. Most of the existing approaches for intermittent fault identification assume that suitable instrumentation has been provided in the program, typically in the form of assertions that dictate which program states are considered to be erroneous, by examining variable values. This approach is, however, inefficient, since only errors for which appropriate instrumentation has been provided will be uncovered. In this paper we propose a method that can be used to detect probable sources of intermittent faults within a program. Our method proposes certain points in the code, whose data interdependencies combined with their execution interweaving indicate that they could be the root cause of intermittent faults. The approach presented in this paper extends our previous work, by examining shared variable access sequences and taking into account not only direct dependencies between shared variables, but additionally indirect ones, i.e. cases where values of local variables are computed using values of some shared variable(s), and subsequently the local variable values are used to set the value of other shared variables. The detection of suspicious access pattern, which may indicate the presence of intermittent faults, is formalized through the introduction of generalized rules; these rules are combined with model-based checking to ensure that all program execution paths are covered. The list of suspicious locations within the code is finally presented to the developer, who will decide after a thorough examination of the code, to accept or reject each of the proposals.

}, keywords = {Fault detection, Intermittent faults, Model-based checking, Shared variables}, issn = {0164-1212}, doi = {10.1016/j.jss.2024.112228}, author = {Sotiropoulos, Panagiotis and Costas Vassilakis} } @article {862, title = {A Machine Learning Framework for Harvesting and Harmonizing Cultural and Touristic Data}, journal = {Information}, volume = {16}, year = {2025}, pages = {1038}, abstract = {

Cultural and touristic information is increasingly available through a multitude of heterogeneous sources, including official repositories, community platforms, and open data initiatives. While prominent landmarks are typically covered across sources, less-known attractions are also documented with varying degrees of detail, resulting in fragmented, overlapping, or complementary content. To enable integrated access to this wealth of information, harvesting and consolidation mechanisms are required to collect, reconcile, and unify distributed content referring to the same entities. This paper presents a machine learning-driven framework for harvesting, homogenizing, and augmenting cultural and touristic data across multilingual sources. Our approach addresses entity resolution, duplication detection, and content harmonization, laying the foundation for enriched, unified representations of attractions and points of interest. The framework is designed to support scalable integration pipelines and can be deployed in applications aimed at tourism promotion, digital heritage, and smart travel services.

}, keywords = {Cultural heritage, data augmentation, data homogenization, digital heritage, Machine Learning, named entity recognition, social media analysis, tourism analytics, trajectory extraction, web scraping}, issn = {2078-2489}, doi = {10.3390/info16121038}, url = {https://www.mdpi.com/2078-2489/16/12/1038}, author = {Deligiannis, Kimon and Tryfonopoulos, Christos and Raftopoulou, Paraskevi and Vassilakis, Costas and Kaffes, Vassilis and Skiadopoulos, Spiros} } @conference {850, title = {MiniLib: A flow analysis{\textendash}based approach for attack surface reduction through software debloating}, booktitle = {Proceedings of the 2025 IEEE International Conference on Cyber Security and Resilience}, year = {2025}, abstract = {

Software applications typically use libraries for the implementation of commonly used tasks. Each library encompasses an extensive collection of functionalities that cover a specific task area, such as interfacing with a database. However, while applications typically use a small subset of these functionalities, the unused ones are also bundled into the final distribution, due to the fact that the libraries are loaded and linked as indivisible objects. The presence of unused functionalities in the executable program increases its attack surface, since attackers may invoke code in these functionalities or exploit their vulnerabilities, using techniques such as stack smashing or buffer overflow. In this paper, we present MiniLib, an approach that removes from the final executable any unused functionalities that may be present in the libraries, reducing attack surface and thus enhancing security. The efficiency of MiniLib is validated through its application on applications drawn from the O-RAN 6G framework.

}, keywords = {6G, Attack surface, Flow-based analysis, Java bytecode, O-RAN, security, Software debloating, Vulnerabilities}, doi = {https://doi.org/10.1109/CSR64739.2025.11129981}, author = {Loukas Kopanias and Panagiotis Sotiropoulos and Nicholas Kolokotronis and Costas Vassilakis} } @article {856, title = {Optimising sustainable digital branding through big data: an analysis of the real estate sector across six continents}, journal = {International Journal of Internet Marketing and Advertising}, volume = {To appear}, year = {2025}, abstract = {

This research investigates effective strategies for optimising corporate digital brand name and reducing digital marketing costs in the real estate industry by leveraging consumer behavioural data from social media and websites, alongside technical performance metrics. Data were collected over 18 months from 10 globally leading real estate companies operating across six continents, using advanced web and social media analytics tools. The first phase of the study focused on extracting behavioural big data and technical metrics, which were subjected to correlation and regression analyses. In the second phase, an agent-based model (ABM) was developed to simulate consumer behaviour and predict digital brand performance and cost savings. Key findings underscore the synergistic potential of integrating social media and search engine advertisements to enhance brand visibility and surpass competitors. Additionally, reducing organic and paid traffic costs requires optimising website design with concise, user-focused content on landing pages to ensure faster response times. This studys predictive framework bridges the gap between big data analytics and sustainable branding, offering actionable insights for real estate practitioners to align their strategies with evolving consumer demands and environmental goals.

}, keywords = {big data, digital brand name, digital costs, digital marketing, real estate, web analytics}, issn = {1741-8100}, doi = {10.1504/IJIMA.2025.10071886}, author = {Reklitis, Dimitrios P. and Terzi, Marina C. and Sakas, Damianos P. and Vassilakis, Costas} } @conference {858, title = {PROVATO: A Data-Centric Edge-AI Architecture forPrecision Livestock Monitoring Using IoT}, booktitle = {Hellenic Data Management Symposium (HDMS)}, year = {2025}, abstract = {

This work presents PROVATO (PRecisiOn liVestock monitoring with AI and IoT tOols), an edge AI and IoTpowered platform for real-time livestock monitoring. The system enables farmers to track animal health and behaviour, ensuring scalable data processing and AI inference at both the edge and the cloud. This approach supports decision-making, reduces resource waste, and improves animal welfare.

}, keywords = {IoT, livestock monitoring, livestock wellfare}, author = {Andreas Doumouras and Evangelos Mitikas and Ermis Doulos and Manos Schoinoplokakis and Giannis Nikolentzos and Christos Tryfonopoulos and Spiros Skiadopoulos and Costas Vassilakis and Paraskevi Raftopoulou*} } @article {851, title = {Security Issues in Brain {\textendash} Computer Interfaces (BCI)}, journal = {Hellenic Journal of Nursing}, volume = {TBD}, year = {2025}, abstract = {

Introduction: Brain-computer interface (BCI) systems emerged to harness and interpret the electrical activity of the brain for interaction with external devices. BCI, or Brain-Machine Interface (BMI), integrates hardware and software to facilitate human-environment interaction, independently of peripheral nerves and muscles, through control signals from electroencephalographic data. However, in the area of ​​security, BCI systems remain underdeveloped. The importance of security in BCI systems has only recently attracted attention, leading to the emergence of terms such as neurosecurity and neuroethics. The literature has identified categories of security threats that affect the integrity and confidentiality of BCI, however, comprehensive research on these issues is still lacking. Purpose: The purpose of this literature review is to describe the potential security attacks that affect each phase of the life cycle of a BCI system. Also, the analysis of the impacts of these attacks as well as the possible countermeasures that can be used and how they are documented based on the international literature. Material and Method: A narrative literature review was conducted based on articles from scientific databases (PubMed /Medline, Google Scholar) using specific keywords in Greek and English, in printed books and online references. Results: A critical review of the literature reveals that the security field focused on BCI system technologies is not yet mature, creating opportunities for malicious actors to launch attacks. Even unsophisticated attacks can however have a significant impact on both BCI system technologies and user security. In addition, the development of standardization initiatives for the unification of BCI systems in terms of information is recognized as an opportunity. Well-studied areas such as implantable medical devices and the Internet of Things can provide guidance for the development of robust security mechanisms, while user awareness of security issues in BCI systems is considered crucial. Conclusions: Significant advances in BCI research have occurred over the past two decades, leveraging established methodologies in signal processing and pattern recognition. Many studies have improved the accuracy of BCI and proposed methods for efficient information transfer, despite challenges in brain signal processing. As a result, user training time has been reduced, facilitating broader application of BCI for people with disabilities, including word processing and neuroprosthetics. Most BCI applications are still in the research phase and are not yet suitable for widespread everyday use. Current limitations include low information transfer rates, variable reliability, and inconvenience due to electrode maintenance requirements and software handling. There are many proposed countermeasures to mitigate risks, but extensive research is still necessary, due to the significant threats associated with these systems.

}, keywords = {Brain-Computer Interfaces, Cybersecurity, Neuroprivacy, Neurosecurity, privacy}, author = {Stathoulis, John D. and Bakalis, Vissarion I. and Costas Vassilakis} } @article {857, title = {Stitching History into Semantics: LLM-Supported Knowledge Graph Engineering for 19th-Century Greek Bookbinding}, journal = {Machine Learning and Knowledge Extraction}, volume = {7}, year = {2025}, pages = {59}, abstract = {

Preserving cultural heritage can be efficiently supported by structured and semantic representation of historical artifacts. Bookbinding, a critical aspect of book history, provides valuable insights into past craftsmanship, material use, and conservation practices. However, existing bibliographic records often lack the depth needed to analyze bookbinding techniques, provenance, and preservation status. This paper presents a proof-of-concept system that explores how Large Language Models (LLMs) can support knowledge graph engineering within the context of 19th-century Greek bookbinding (1830{\textendash}1900), and as a result, generate a domain-specific ontology and a knowledge graph. Our ontology encapsulates materials, binding techniques, artistic styles, and conservation history, integrating metadata standards like MARC and Dublin Core to ensure interoperability with existing library and archival systems. To validate its effectiveness, we construct a Neo4j knowledge graph, based on the generated ontology and utilize Cypher Queries{\textemdash}including LLM-generated queries{\textemdash}to extract insights about bookbinding practices and trends. This study also explores how semantic reasoning over the knowledge graph can identify historical binding patterns, assess book conservation needs, and infer relationships between bookbinding workshops. Unlike previous bibliographic ontologies, our approach provides a comprehensive, semantically rich representation of bookbinding history, methods and techniques, supporting scholars, conservators, and cultural heritage institutions. By demonstrating how LLMs can assist in ontology/KG creation and query generation, we introduce and evaluate a semi-automated pipeline as a methodological demonstration for studying historical bookbinding, contributing to digital humanities, book conservation, and cultural informatics. Finally, the proposed approach can be used in other domains, thus, being generally applicable in knowledge engineering.

}, keywords = {bookbinding history, Cultural heritage, knowledge graphs, large language models, ontology engineering}, issn = {2504-4990}, doi = {https://doi.org/10.3390/make7030059}, author = {Doumanas, Dimitrios and Ntalouka, Efthalia and Vassilakis, Costas and Wallace, Manolis and Kotis, Konstantinos} } @conference {859, title = {On the use of pharmacies to establish a defibrillator network}, booktitle = {20th International Workshop on Semantic and Social Media Adaptation and Personalization}, year = {2025}, keywords = {Defibrillator network, Pharmacies, Population coverage}, author = {Manolis Wallace and Christos Champilomatis and Panagiota Ventirozou and Georgios Pappas and Vasssilis Poulopoulos and Costas Vassilakis} } @article {854, title = {Using Prediction Confidence Factors to Enhance Collaborative Filtering Recommendation Quality}, journal = {Technologies}, volume = {13}, year = {2025}, pages = {181}, abstract = {

Recommender systems suggest items that users are likely to accept by predicting ratings for items they have not already rated. Collaborative filtering is a widely used method that produces these predictions, based on the ratings of similar users, termed as near neighbors. However, in many cases, prediction errors occur and, therefore, the recommender system ends up either recommending unwanted products or missing out on products the user would actually desire. As a result, the quality of the recommendations that are produced is of major importance. In this paper, we introduce an advanced collaborative filtering recommendation algorithm that upgrades the quality of the recommendations that are produced by considering, along with the rating prediction value of the items computed by the plain collaborative filtering procedure, a number of confidence factors that each rating prediction fulfills. The presented algorithm maintains high recommendation coverage, and can be applied to every collaborative filtering dataset, since it is based only on the very basic information. Based on the application of the algorithm on widely used recommender systems datasets, the proposed algorithm significantly upgrades the recommendation quality, surpassing the performance of state-of-the-art research works that also consider confidence factors.

}, keywords = {Algorithm, collaborative filtering, prediction confidence factors, recommendation quality, Recommender Systems}, issn = {2227-7080}, doi = {https://doi.org/10.3390/technologies13050181}, url = {https://doi.org/10.3390/technologies13050181}, author = {Dionisis Margaris and Spiliotopoulos, Dimitris and Sgardelis, Kiriakos and Costas Vassilakis} } @article {845, title = {Virtual Cultural Experiences for the Elderly: Formative Studies and First Findings Regarding Cultural Content}, journal = {Applied Sciences}, volume = {15}, year = {2025}, month = {February}, pages = {1820}, abstract = {

In societies with aging populations, the active participation of elders in all aspects of societal life is crucial. Cultural heritage provides a rich vehicle for engaging elders, stimulating both cognitive and affective responses, and keeping human brains active. This study focused on gathering requirements for creating content for virtual cultural experiences. Specifically, participants were shown various images and a film, and their self-reported thoughts and emotions were collected. The images were chosen by experts for the specific emotions they could trigger. The same images were analyzed with sentiment analysis software and finally given to the elders to express their emotions. The results of sentiment analysis, the analysis of experts, and the data from the participants were compared, showing differences between the perceived emotions. Regarding the historical film, the participants discussed the main emotions they experienced. The results were analyzed to extract guidelines for the content creation of VR applications.

}, keywords = {content requirements, elders, Virtual reality}, issn = {2076-3417}, doi = {10.3390/app15041820}, author = {Antoniou, Angeliki and Costas Vassilakis and Kantianis, Georgios and Sylaiou, Stella and Kolokithas, George} } @article {842, title = {Artificial Intelligence Tools for the Agriculture Value Chain: Status and Prospects}, journal = {Electronics}, volume = {13}, year = {2024}, pages = {4362}, abstract = {

This article explores the transformative potential of artificial intelligence (AI) tools across the agricultural value chain, highlighting their applications, benefits, challenges, and future prospects. With global food demand projected to increase by 70\% by 2050, AI technologies{\textemdash}including machine learning, big data analytics, and the Internet of things (IoT){\textemdash}offer critical solutions for enhancing agricultural productivity, sustainability, and resource efficiency. The study provides a comprehensive review of AI applications at multiple stages of the agricultural value chain, including land use planning, crop selection, resource management, disease detection, yield prediction, and market integration. It also discusses the significant challenges to AI adoption, such as data accessibility, technological infrastructure, and the need for specialized skills. By examining case studies and empirical evidence, the article demonstrates how AI-driven solutions can optimize decision-making and operational efficiency in agriculture. The findings underscore AI{\textquoteright}s pivotal role in addressing global agricultural challenges, with implications for farmers, agribusinesses, policymakers, and researchers. This article aims to advance the evolving research and discussions on sustainable agriculture, contributing insights that promote the adoption of AI technologies and influence the future of farming.

}, keywords = {artificial intelligence, precision agriculture, sustainability, value chain}, issn = {2079-9292}, doi = {10.3390/electronics13224362}, author = {Assimakopoulos, Fotis and Costas Vassilakis and Dionisis Margaris and Kotis, Konstantinos and Spiliotopoulos, Dimitris} } @article {837, title = {Challenges and Trends in Student Evaluation of Teaching: Analysis of SET Data from the University of Peloponnese}, journal = {Information}, volume = {15}, year = {2024}, month = {09/2024}, pages = {576}, abstract = {

This study examines the effectiveness of Student Evaluations of Teaching at the University of Peloponnese, which has systematically collected anonymous evaluations since 2015. The analysis focused on participation rates, average scores, and the correlation between student evaluations and their academic performance. Participation rates were notably low, averaging 14.63\%, with postgraduate students showing higher rates (27.33\%) than undergraduates (10.77\%). The average SET scores were moderately high, with postgraduates rating their courses slightly better (M = 4.137) than undergraduates (M = 3.899). A weak positive correlation was found between course grades and evaluations among undergraduates, whereas no significant correlation was observed for postgraduates. These findings highlight challenges in using SETs as reliable measures of teaching effectiveness and suggest the need for improved participation and more comprehensive evaluation methods. The results provide insights into enhancing assessment practices and contribute to the broader discourse on the validity of student evaluations in higher education.

}, keywords = {Higher Education, quality assurance, SET}, issn = {2078-2489}, doi = {10.3390/info15090576}, author = {Papadogiannis, Ilias and Costas Vassilakis and Wallace, Manolis and Katsis, Athanassios} } @conference {838, title = {Estimating MPdist with SAX and Machine Learning}, booktitle = {New Trends in Database and Information Systems (Proceedings of ADBIS 2024, Short Papers, Workshops, Doctoral Consortium and Tutorials)}, year = {2024}, publisher = {Springer Cham}, organization = {Springer Cham}, abstract = {

MPdist is a distance measure which considers two time series to be similar if they share many similar subsequences. However, computing MPdist can be slow, especially for large time series. We propose a technique for the approximate computation of MPdist that uses the SAX representation of the time series to quickly estimate the Nearest Neighbor (NN) distance of each subsequence, and then applies a Machine Learning model to correct the accuracy loss incurred. Our method is orders of magnitude faster than the exact computation of MPdist; at the same time, our best approximation computes the NN of a time series with high accuracy. A thorough evaluation of our technique is provided.

}, keywords = {Distance metric, Machine Learning, MPdist, Random Forest, SAX, Time series}, doi = {https://doi.org/10.1007/978-3-031-70421-5_32}, author = {Mihalis Tsoukalos and Pantelis Chronis and Nikos Platis and Costas Vassilakis}, editor = {Joe Tekli and Johann Gamper and Richard Chbeir and Yannis Manolopoulos and Salma Sassi and Mirjana Ivanovic and Vargas-Solar, Genoveva and Ester Zumpano} } @article {833, title = {Experimental results for Evaluating User Similarity Metrics in Sparse Collaborative Filtering Datasets}, number = {TR-24001}, year = {2024}, month = {03/2024}, institution = {SODA lab}, type = {Technical Report}, address = {Tripolis, Greece}, keywords = {collaborative filtering, Evaluation, Sparse Datasets, User similarity metrics}, issn = {SODA-TR-24001}, author = {Kiriakos Sgardelis and Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @article {841, title = {Exploiting Rating Prediction Certainty for Recommendation Formulation in Collaborative Filtering}, journal = {Big Data and Cognitive Computing}, volume = {8}, year = {2024}, pages = {53}, abstract = {

Collaborative filtering is a popular recommender system (RecSys) method that produces rating prediction values for products by combining the ratings that close users have already given to the same products. Afterwards, the products that achieve the highest prediction values are recommended to the user. However, as expected, prediction estimation may contain errors, which, in the case of RecSys, will lead to either not recommending a product that the user would actually like (i.e., purchase, watch, or listen) or to recommending a product that the user would not like, with both cases leading to degraded recommendation quality. Especially in the latter case, the RecSys would be deemed unreliable. In this work, we design and develop a recommendation algorithm that considers both the rating prediction values and the prediction confidence, derived from features associated with rating prediction accuracy in collaborative filtering. The presented algorithm is based on the rationale that it is preferable to recommend an item with a slightly lower prediction value, if that prediction seems to be certain and safe, over another that has a higher value but of lower certainty. The proposed algorithm prevents low-confidence rating predictions from being included in recommendations, ensuring the recommendation quality and reliability of the RecSys.

}, keywords = {Algorithm, collaborative filtering, confidence, Evaluation, Rating Predictions, Recommender Systems, Uncertainty}, issn = {2504-2289}, doi = {10.3390/bdcc8060053}, author = {Dionisis Margaris and Sgardelis, Kiriakos and Spiliotopoulos, Dimitris and Costas Vassilakis} } @article {836, title = {The Implementation of {\textquotedblleft}Smart{\textquotedblright} Technologies in the Agricultural Sector: A Review}, journal = {Information}, volume = {15}, year = {2024}, pages = {466}, abstract = {

The growing global population demands an increase in agricultural production and the promotion of sustainable practices. Smart agriculture, driven by advanced technologies, is crucial to achieving these goals. These technologies provide real-time information for crop monitoring, yield prediction, and essential farming functions. However, adopting intelligent farming systems poses challenges, including learning new systems and dealing with installation costs. Robust support is crucial for integrating smart farming into practices. Understanding the current state of agriculture, technology trends, and the challenges in technology acceptance is essential for a smooth transition to Agriculture 4.0. This work reports on the pivotal synergy of IoT technology with other research trends, such as weather forecasting and robotics. It also presents the applications of smart agriculture worldwide, with an emphasis on government initiatives to support farmers and promote global adoption. The aim of this work is to provide a comprehensive review of smart technologies for precision agriculture and especially of their adoption level and results on the global scale; to this end, this review examines three important areas of smart agriculture, namely field, greenhouse, and livestock monitoring.

}, keywords = {Agriculture 4.0, IoT, precision agriculture, smart farming}, issn = {2078-2489}, doi = {https://doi.org/10.3390/info15080466}, url = {https://www.mdpi.com/2078-2489/15/8/466}, author = {Assimakopoulos, Fotis and Costas Vassilakis and Dionisis Margaris and Kotis, Konstantinos and Spiliotopoulos, Dimitris} } @conference {839, title = {Improving Recommendation Quality in Collaborative Filtering by Including Prediction Confidence Factors}, booktitle = {Proceedings of the 20th International Conference on Web Information Systems and Technologies (WEBIST 24)}, year = {2024}, publisher = {SCITEPRESS Digital Library}, organization = {SCITEPRESS Digital Library}, abstract = {

Collaborative filtering is a prevalent recommender system technique which generates rating predictions based on the rating values given by the users{\textquoteright} near neighbours. Consequently, for each user, the items scoring the highest prediction values are recommended to them. Unfortunately, predictions inherently entail errors, which, in the case of recommender systems, manifest as unsuccessful recommendations. However, along with each rating prediction value, prediction confidence factors can be computed. As a result, items having low prediction confidence factor values, can be either declined for recommendation or have their recommendation priority demoted. In the former case, some users may receive fewer recommended items or even none, especially when using a sparse dataset. In this paper, we present an algorithm that determines the items to be recommended by considering both the rating prediction values and confidence factors of predictions, allowing for predictions with higher confidence factors to outrank predictions with higher value, but lower confidence. The presented algorithm achieves to enhance the recommendation quality, while at the same time retaining the number of recommendations for each user.

}, keywords = {Algorithm, Certainty factors, collaborative filtering, Rating Predictions, Recommender Systems}, author = {Kiriakos Sgardelis and Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis and Stefanos Ougiaroglou} } @conference {840, title = {Predicting Agricultural Product and Supplies Prices using Artificial Intelligence}, booktitle = {Proceedings of the 16th International Conference on Knowledge Management and Information Systems}, year = {2024}, publisher = {SCITEPRESS Digital Library}, organization = {SCITEPRESS Digital Library}, abstract = {

This work focuses on the prediction of agricultural product and supply prices using historical data and artificial intelligence methods. Agricultural product and supply prices are important for the economy and growth of agriculture. Using modern data analysis and deep learning methods, a forecasting model was developed to help us predict future price trends. The data used include the sales prices of crop products and the purchase prices of agricultural inputs. The developed forecasting methods exhibit high accuracy for predicting the actual prices of products and supplies, with error margins ranging from 0.29\% to 9.8\%, while they can also predict price rises and falls, with respective success rates ranging from 73.29\% to 84.96\%.

}, keywords = {Agricultural Products, Data Integration, deep learning, Forecasting Models, Machine Learning, Price Forecasting}, author = {Ioannis Dionissopoulos and Fotis Assimakopoulos and Dimitris Spiliotopoulos and Dionisis Margaris and Costas Vassilakis} } @article {835, title = {On the Quality and Validity of Course Evaluation Questionnaires Used in Tertiary Education in Greece}, journal = {Trends in Higher Education}, volume = {3}, year = {2024}, pages = {221{\textendash}234}, abstract = {

In compliance with national legislation, Greek tertiary education institutions assess educational quality often using a standardized anonymous questionnaire completed by students. This questionnaire aims to independently evaluate various course components, including content organization, instructor quality, facilities, infrastructure, and grading methods. Despite widespread use across universities, the questionnaire{\textquoteright}s validity remains unexamined. This study addresses this gap by analyzing 48,000+ questionnaire responses from the University of the Peloponnese (2014{\textendash}2022), encompassing 68 undergraduate and graduate programs. Confirmatory factor analyses were used to assess the quality of the questionnaire, while exploratory factor analyses were used to assess the dimensions of the tool based on the data. Both analyses reveal shortcomings: confirmatory analysis detects strong correlations between supposedly different factors, and exploratory analysis identifies dimensions inconsistent with the expected structure. These findings question the questionnaire{\textquoteright}s quality and the validity of drawn conclusions, while additionally identifying opportunities for reducing the number of questions, which can contribute to increased questionnaire submission rates. Given its common use across Greek universities and its influence on shaping courses, urgent redesigning of the questionnaire for tertiary education evaluation is recommended.

}, keywords = {CFA, EFA, Higher Education, quality assurance}, doi = {https://doi.org/10.3390/higheredu3020013}, url = {https://www.mdpi.com/2813-4346/3/2/13}, author = {Papadogiannis, Ilias and Costas Vassilakis and Wallace, Manolis and Katsis, Athanassios} } @article {827, title = {An Assessment of the Effectiveness of the Remedial Teaching Education Policy}, journal = {Knowledge}, volume = {3}, year = {2023}, month = {jul}, pages = {349{\textendash}363}, abstract = {

The remedial teaching policy is a flagship education policy of the Greek Ministry of Education that aims to create a school of equal opportunities by providing additional support to students from disadvantaged social backgrounds. In this work we utilised a data set provided by the Ministry of Education, followed a black box approach and built on previous results in order to achieve the first ever evaluation, based on data, of the remedial teaching policy. Our findings indicate that remedial teaching is very effective in supporting very weak students, helping 70\% of them achieve better academic performance and one out of three of them to sustain this enhanced academic performance in the future, long after they have stopped receiving remedial teaching. On the other hand, and contrary to what is widely believed, our results show that remedial teaching has the opposite impact to what it was designed for, as it is primarily the privileged students that receive the benefits. Consequently, in the way it is currently implemented, remedial teaching widens the gap between privileged and disadvantaged students rather than reduces it. The implications of the work are wide and far reaching, including the establishment of the need to revisit the way remedial teaching is implemented, the highlighting of the value in the data gathered by the Ministry of Education and the proof that individual educational policies can be objectively assessed despite being part of a complex system in which multiple education policies are implemented concurrently.

}, keywords = {black box evaluation, data driven evaluation, education policy, remedial teaching}, doi = {https://doi.org/10.3390/knowledge3030024}, url = {https://doi.org/10.3390/knowledge3030024}, author = {Ilias Papadogiannis and Manolis Wallace and Vassilis Poulopoulos and Costas Vassilakis and Georgios Lepouras and Nikos Platis} } @article {831, title = {Blockchain meets Internet of Things (IoT) forensics: A unified framework for IoT ecosystems}, journal = {Internet of Things}, year = {2023}, month = {oct}, pages = {100968}, abstract = {

With the continuously increasing number of security incidents targeting sensors, embedded devices, and other electronics appliances and systems that comprise the so-called Internet of things (IoT), the field of IoT forensics emerged as a branch of digital forensics focusing on the investigation of attacks in the IoT ecosystem. Digital evidence authenticity, integrity, confidentiality, and privacy are among the factors affecting the investigation process in IoT forensics, which can be addressed by employing the blockchain as the means not only for the preservation of digital evidence, but also for other steps of a digital forensics investigation process. The high-level goal of the paper is three-fold: to establish a holistic IoT forensics process as a reference point against which blockchain integration patterns and best practices will be identified in order to yield a robust, widely accepted and scalable architecture of the blockchain-enabled solution; to integrate the blockchain with the proposed IoT forensics process for addressing the above challenges; and to evaluate the overall solution highlighting improvements and potential performance bottlenecks. The proposed blockchain-enabled platform leverages multi-access edge computing and has been implemented with Hyperledger Fabric on an extensive virtualized testbed providing a realistic smart home environment. A thorough evaluation was conducted with real cyber-attacks generating digital evidence at high rates for testing the platform{\textquoteright}s behavior at high load. The experimental results showed that the proposed platform achieved high throughput, excessively low latency, and zero error rate in the operation of the blockchain network.

}, keywords = {blockchain, cyber-security, Digital forensics, Edge computing, Internet of Things}, doi = {10.1016/j.iot.2023.100968}, url = {https://www.sciencedirect.com/science/article/pii/S2542660523002913}, author = {Sotirios Brotsis and Konstantinos P. Grammatikakis and Dimitrios Kavallieros and Antonio I. Mazilu and Nicholas Kolokotronis and Konstantinos Limniotis and Costas Vassilakis} } @article {828, title = {Chatbots for Cultural Venues: A Topic-Based Approach}, journal = {Algorithms}, volume = {16}, year = {2023}, month = {jul}, pages = {339}, abstract = {

Digital assistants{\textemdash}such as chatbots{\textemdash}facilitate the interaction between persons and machines and are increasingly used in web pages of enterprises and organizations. This paper presents a methodology for the creation of chatbots that offer access to museum information. The paper introduces an information model that is offered through the chatbot, which subsequently maps the museum{\textquoteright}s modeled information to structures of DialogFlow, Google{\textquoteright}s chatbot engine. Means for automating the chatbot generation process are also presented. The evaluation of the methodology is illustrated through the application of a real case, wherein we developed a chatbot for the Archaeological Museum of Tripolis, Greece.

}, keywords = {chatbots, cultural venues, Museums, RDF triples, topics}, doi = {10.3390/a16070339}, url = {https://doi.org/10.3390/a16070339}, author = {Vasilis Bouras and Dimitris Spiliotopoulos and Dionisis Margaris and Costas Vassilakis and Konstantinos Kotis and Angeliki Antoniou and George Lepouras and Manolis Wallace and Vassilis Poulopoulos} } @article {818, title = {Disruptive Technologies for Parliaments: A Literature Review}, journal = {Future Internet}, volume = {15}, year = {2023}, month = {feb}, pages = {66}, abstract = {

Exploitation and use of disruptive technologies, such as the Internet of Things, recommender systems, and artificial intelligence, with an ambidextrous balance, are a challenge, nowadays. Users of the technologies, and stakeholders, could be part of a new organisational model that affects business procedures and processes. Additionally, the use of inclusive participatory organisational models is essential for the effective adoption of these technologies. Such models aim to transform organisational structures, as well. Public organisations, such as the parliament, could utilise information systems{\textquoteright} personalisation techniques. As there are a lot of efforts to define the framework, the methodology, the techniques, the platforms, and the suitable models for digital technologies adoption in public organisations, this paper aims to provide a literature review for disruptive technology inclusive use in parliaments. The review emphasises the assessment of the applicability of the technologies, their maturity and usefulness, user acceptance, their performance, and their correlation to the adoption of relevant innovative, inclusive organisational models. It is argued that the efficient digital transformation of democratic institutions, such as parliaments, with the use of advanced e-governance tools and disruptive technologies, requires strategic approaches for adoption, acceptance, and inclusive service adaptation.

}, keywords = {artificial intelligence, digital transformation, inclusiveness, Internet of Things, parliament, Recommender Systems}, doi = {https://doi.org/10.3390/fi15020066}, url = {https://www.mdpi.com/1999-5903/15/2/66}, author = {Dimitris Koryzis and Dionisis Margaris and Costas Vassilakis and Konstantinos Kotis and Dimitris Spiliotopoulos} } @conference {826, title = {EnQuest: A Cloud Datalake Infrastructure for Heterogeneous Analytics in Maritime and Tourism Domains}, booktitle = {DATA 2023 (demo)}, year = {2023}, abstract = {

Within recent years, transportation and supply chain have been affected by an avalanche of data including IoT devices, online services, social media and others. However, the implemented solutions so far are fragmented, physically distributed, require specialized IT knowledge to deploy, and involve significant IT experience to operate even for trivial tasks. In the context of the ENIRISST+ project, we developed EnQuest1, an online data lake that allows users without any IT background to harvest, store, organize, analyze and share heterogeneous, multi-faceted maritime/tourism data. EnQuest provides a zero-administration, zero-cost, integrated framework that enables scientists, practitioners and other stakeholders within the above domains to easily: (i) deploy data acquisition services (crawlers, dataset imports, questionnaire forms), (ii) design and manage versatile customizable data stores, (iii) share whole datasets or horizontal/vertical data shards with other stakeholders, (iv) search, filter and analyze data via an expressive yet simple-to-use graphical query engine and visualization tools, and (v) perform user management and access control operations on the stored data. To the best of our knowledge, this is the first approach in the literature that targets users without an IT background and focuses on collecting, managing, analyzing, and sharing diverse, multi-faceted data in maritime the and tourism sectors. The main goals of the proposed demonstration are to showcase the EnQuest system to the conference participants and promote the work of the ENIRISST+ project consortium. During the demo we will (i) deploy social media crawlers to gather maritime data and show the participants how to process and visualise them, (ii) create live questionnaires using the EnQuest functionality, ask the participants to fill them in and demonstrate the live processed data on appropriate dashboards, and (iii) demonstrate how to import data and subscribe to data flows of other users through the implemented publish/subscribe module. For the needs of the demo we will only require internet connection and a desk; we will have our own laptops to use at the demonstration.

}, keywords = {big data, cloud systems, data analytics, datalakes, maritime, tourism}, author = {Kimon Deligiannis and Christos Tryfonopoulos and Paraskevi Raftopoulou and Nikos Platis and Costas Vassilakis} } @conference {829, title = {Estimating \iSAX Parameters for Efficiency}, booktitle = {New Trends in Database and Information Systems (Proceedings of the 2023 European Conference on Advances in Databases and Information Systems / ADBIS 2023)}, year = {2023}, publisher = {Springer Nature Switzerland}, organization = {Springer Nature Switzerland}, address = {Cham}, abstract = {

\iSAX is considered one of the most efficient indexes for time series. Several parameters affect the construction of an \iSAX index: the sliding window size, the threshold value, the number of segments and the maximum cardinality, the last two being related to the SAX representation. In this paper (i) we consider the effect of each parameter on the efficiency of the \iSAX index, (ii) we evaluate the importance of each parameter, and, (iii) suggest how to optimize these parameters.

}, keywords = {Indexing, Parameter tuning, SAX, Time series}, isbn = {978-3-031-42941-5}, doi = {10.1007/978-3-031-42941-5_1}, author = {Tsoukalos, Michalis and Platis, Nikos and Costas Vassilakis} } @conference {825, title = {Estimating \iSAX Parameters for Efficiency}, booktitle = {Proceedings of the 27th European Conference on Advances in Databases and Information Systems (ADBIS 2023)}, year = {2023}, abstract = {

\iSAX is considered one of the most efficient indexes for time series. Several parameters affect the construction of an \iSAX index: the sliding window size, the threshold value, the number of segments and the maximum cardinality, the last two being related to the SAX representation. In this paper (i) we consider the effect of each parameter on the efficiency of the \iSAX index, (ii) we evaluate the importance of each parameter, and, (iii) suggest how to optimize these parameters.

}, keywords = {Indexing, Parameter tuning, SAX, Time series}, author = {Tsoukalos, Michalis and Platis, Nikos and Costas Vassilakis} } @conference {824, title = {Implementing the infrastructure for Dimitris Papaioannou{\textquoteright}s archive:approaching the degrees of separation in his work}, booktitle = {DARIAH 2023 (poster presentation)}, year = {2023}, abstract = {

Creating the infrastructure for an archive is considered, nowadays, to be a trivial procedure. Several tools (e.g. Omeka [2], CollectiveAccess[3], CollectionSpace[4]) and prototypes (eg. Dublin Core [5], VRA CORE [6]) are available for use in order to, either directly install and use a CMS for cultural related data (first case), or build a system {\textquotedblleft}from scratch{\textquotedblright} based on a common prototype (second case). This procedure would lead to the digitization of at least an archive{\textquoteright}s metadata and to the organization of the archive itself; it would offer the ability to search for information in the archive in an easy way, it would allow people to access the information of the archive, and it could also be part of a larger cultural data lake (Europeana). The solutions for these use cases, are extant, present and available. On the other hand, occasionally one comes across archives of artists that have a special view of art, are ahead of their time, design their own universe, and they keep evolving it throughout their life. In this paper, we discuss the implementation of the archive for Dimitiris Papaioannou, a diverse archive which includes several different types of data. In this case, we have selected a special approach, in order to fully capture the artistic aspects of the archive{\textquoteright}s content, which was analyzed in the context of the GENESIS project [1]. Throughout this project, the procedure through which the artist approaches the performance arts and generates ideas was recorded and analyzed. Following the aforementioned analysis, the archive material provides insight for the artist{\textquoteright}s visual arts, his dancing roads and his performances, and unveils his approach to performance arts (or art, in general). Then, the archive is structured in a way that would allow all archive visitors, including the general public as well as researchers, to obtain information about the individual elements of the work, but also locate the {\textquotedblleft}genetic material{\textquotedblright} of the artist into the archive. To achieve this goal, interdisciplinary research involving the cooperation of scientists and researchers from both the humanities and the technology domains was required. The research team designed an information layer entailing objective information (e.g. works, performances, participants and their roles etc.) and subjective information (e.g. tagging or free text descriptions), and accommodating semantic links between them. Metadata were also associated to information items, where applicable. The information layer fully serves the needs for information search and retrieval, while it additionally provides the underpinnings for data mining procedures that can possibly reveal patterns or data correlations that have remained unobserved.

}, keywords = {cultural informatics, Cultural Metadata, Cultural Semantics, Performance art}, author = {Vassilis Poulopoulos and Eleni Papalexiou and Costas Vassilakis and Avra Xepapadakou and Valia Vraka} } @conference {822, title = {Minimizing Software-Rooted Risk through Library Implementation Selection}, booktitle = {Proceedings of the 2023 IEEE CSR Workshop on Data Science for Cyber Security (DS4CS)}, year = {2023}, abstract = {

In contemporary Internet of Things (IoT) systems, complex software artifacts are deployed to realize the required functionalities. The business logic of these software artifacts is uniquely composed through code that is customly developed according to the requirements, while all software artifacts utilize libraries that implement generic functionalities, which are needed in the context of the realized operations. Libraries, however, often entail vulnerabilities, which may be exploited by threat agents to attack the system. In many cases, the functionality required by an application is realized by a number of alternative libraries, with each library having its own list of vulnerabilities, while differentiations in other non-functional properties (e.g. execution efficiency, memory footprint etc.) may also be present. In this paper, we present an approach for automating the task of minimizing the risk level of IoT systems that is owing to the vulnerabilities of libraries required by software artifacts. The proposed approach exploits knowledge on which libraries provide equivalent implementations of the same functionalities, and automatically assesses the risk level of candidate library combinations and finally selects the library configuration exhibiting the minimum risk level to bundle into the executable software artifact. Additionally, the risk level of candidate implementations is constantly monitored for new vulnerability identifications or fixes in the implementations, triggering new risk assessments and producing new executables as appropriate. The proposed approach can be used in IoT platform deployment to minimize the software-rooted risk level.

}, author = {Panagiotis Sotiropoulos and Christos-Minas Mathas and Costas Vassilakis and Nicholas Kolokotronis} } @article {820, title = {Rating Prediction Quality Enhancement in Low-Density Collaborative Filtering Datasets}, journal = {Big Data and Cognitive Computing}, volume = {7}, year = {2023}, month = {mar}, pages = {59}, abstract = {

Collaborative filtering has proved to be one of the most popular and successful rating prediction techniques over the last few years. In collaborative filtering, each rating prediction, concerning a product or a service, is based on the rating values that users that are considered {\textquotedblleft}close{\textquotedblright} to the user for whom the prediction is being generated have given to the same product or service. In general, {\textquotedblleft}close{\textquotedblright} users for some user u correspond to users that have rated items similarly to u and these users are termed as {\textquotedblleft}near neighbors{\textquotedblright}. As a result, the more reliable these near neighbors are, the more successful predictions the collaborative filtering system will compute and ultimately, the more successful recommendations the recommender system will generate. However, when the dataset{\textquoteright}s density is relatively low, it is hard to find reliable near neighbors and hence many predictions fail, resulting in low recommender system reliability. In this work, we present a method that enhances rating prediction quality in low-density collaborative filtering datasets, by considering predictions whose features are associated with high prediction accuracy as additional ratings. The presented method{\textquoteright}s efficacy and applicability are substantiated through an extensive multi-parameter evaluation process, using widely acceptable low-density collaborative filtering datasets.

}, keywords = {collaborative filtering, Evaluation, low density datasets, personalization, rating prediction quality, Recommender Systems, reliability}, doi = {10.3390/bdcc7020059}, url = {https://www.mdpi.com/2504-2289/7/2/59}, author = {Dionisis Margaris and Costas Vassilakis and Dimitris Spiliotopoulos and Stefanos Ougiaroglou} } @conference {821, title = {RoG: A Pipeline for Automated Sensitive Data Identification and Anonymisation}, booktitle = {Proceedings of the 2023 IEEE CSR Workshop on Data Science for Cyber Security (DS4CS)}, year = {2023}, abstract = {

Nowadays, the amount of data available online is constantly increasing. This data may contain sensitive or private information that can expose the person behind the data or be misused by malicious actors for identity theft, stalking, and other nefarious purposes. There is thus, a growing need to protect individuals{\textquoteright} privacy and prevent data breaches in several application domains. Protecting data privacy though, is a complex and multifaceted issue that involves a range of legal, ethical, and technical considerations. In this paper, we discuss the challenges associated with data protection, the role of automated tools, and the effectiveness of identifying and anonymising sensitive data. We then, propose a fully-automated process for sensitive data identification and anonymisation, based on Natural Language Processing (NLP) techniques, that can be applied both in big diverse datasets and to a wide range of domains.

}, keywords = {anonymisation, automated process, k-anonymity, NER, NLP, pipeline, sensitive/private data}, author = {Sotiris Nikoletos and Stefanos Vlachos and Efstathios Zaragkas and Costas Vassilakis and Christos Tryfonopoulos and Paraskevi Raftopoulou} } @conference {819, title = {SodaSense: An Intelligence Platform for Micro-Mobility, Micro-Climate and Agriculture}, booktitle = {Proceedings of the GEOProcessing 2023}, year = {2023}, abstract = {

SODASENSE is an end-to-end big data manipulation platform that focuses on decision and policy making. It concerns the management of big trajectory and spatio-temporal data that is collected from sensors and relates to micro-mobility, microclimate and agriculture, and aims to the creation of an expert decision making platform with research, social and business orientation.

}, keywords = {big data management and analysis, spatial time series, trajectories}, author = {Paraskevi Raftopoulou and Spiros Skiadopoulos and Christos Tryfonopoulos and Costas Vassilakis} } @article {823, title = {A Software Vulnerability Management Framework for the Minimization of System Attack Surface and Risk}, journal = {Electronics}, volume = {12}, year = {2023}, month = {may}, pages = {2278}, abstract = {

Current Internet of Things (IoT) systems comprise multiple software systems that are deployed to provide users with the required functionalities. System architects create system blueprints and draw specifications for the software artefacts that are needed; subsequently, either custom-made software is developed according to these specifications and/or ready-made COTS/open source software may be identified and customized to realize the overall system goals. All deployed software however may entail vulnerabilities, either due to insecure coding practices or owing to misconfigurations and unexpected interactions. Moreover, software artefacts may implement a much broader set of functionalities than may be strictly necessary for the system at hand, in order to serve a wider range of needs, and failure to appropriately configure the deployed software to include only the required modules results in the further increase of the system attack surface and the associated risk. In this paper, we present a software vulnerability management framework which facilitates (a) the configuration of software to include only the necessary features, (b) the execution of security-related tests and the compilation of platform-wide software vulnerability lists, and (c) the prioritization of vulnerability addressing, considering the impact of each vulnerability, the associated technical debt for its remediation, and the available security budget. The proposed framework can be used as an aid in IoT platform implementation by software architects, developers, and security experts.

}, keywords = {IoT systems, risk management, software vulnerabilities, system design, system security, technical debt}, doi = {10.3390/electronics12102278}, url = {https://doi.org/10.3390/electronics12102278}, author = {Panagiotis Sotiropoulos and Christos-Minas Mathas and Costas Vassilakis and Nicholas Kolokotronis} } @conference {830, title = {A User Interface for Tuning QoS parameters in Recommendation-Based Business Process Scenario Adaptation}, booktitle = {Proceedings of the 19th International Conference on Web Information Systems and Technologies (WEBIST 2023)}, year = {2023}, abstract = {

The Web Services Business Process Execution Language (BPEL) is a special-purpose language that orchestrates web services into a high-level business process. A typical BPEL scenario contains invocations to preselected web services, along with their parameters. However, many recent research works support dynamic service selection, based on user-set policies and criteria. Furthermore, users may request a service recommendation, in which case functionally equivalent service offerings by different providers will be considered by the personalization module. Along with the recommendation request, users provide the policy parameters, which include minimum and maximum bounds for the non-functional attributes concerning the service, and the system exploits these bounds to select and use the optimal candidate services. However, in many real-life cases, a person will accept/purchase a product or a service that exceeds the threshold(s) that initially he/she has set, e.g. if the overhead is marginal or the offer is deemed appealing, or no satisfactory service candidates are identified using the initial settings. In this paper, we present and evaluate a specialized User Interface that allows the user to review service candidates marginally exceeding the specified bounds, and consider them while making the final service selection.

}, keywords = {adaptation, business processes, Personalisation, Recommendation, Recommender Systems, UI, Web services, WS-BPEL}, author = {Kiriakos Sgardelis and Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @article {814, title = {The additional testsuite framework: facilitating software testing and test management}, journal = {International Journal of Web Engineering and Technology}, volume = {TBD}, year = {2022}, abstract = {

In this paper, we present the Additional Testsuite Framework, a novel test suite management approach, which provides structures and instrumentation for the creation, maintenance, evolution and use of test suites for software programs. In particular, the tests can be maintained in a centralized repository, and are developed and maintained independently of specific versions of the associated software. Through the use of annotations, tests are categorized and distributed to the desired versions of the software. The presented framework also supports test-based development, dynamic/selective program builds, feature-based builds, testing in different environments and source code analysis. The Additional Testsuite Framework concept has been implemented and extensively evaluated, with the test cases notably including the JBoss EAP CE and OpenLiberty servers.

}, keywords = {Additional Testsuite Framework, Dynamic Testing, Feature-based testing, Internet application testing, Multiple Environment Testing, Multiversion Testing, Test program repository, Test-Driven Development, Testsuite Management}, author = {Sotiropoulos, Panagiotis and Costas Vassilakis} } @conference {810, title = {Anchoring Effect Mitigation for Complex Recommender System Design}, booktitle = {Proceedings of the 2022 HCI International Conference}, year = {2022}, keywords = {Information/knowledge design/visualization, mental-model, Metaphor, navigation design, Service Design}, author = {Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @article {811, title = {The Effects of Logistics Websites{\textquoteright} Technical Factors on the Optimization of Digital Marketing Strategies and Corporate Brand Name}, journal = {Processes}, volume = {10}, year = {2022}, month = {may}, pages = {892}, keywords = {advertising, big data, brand name, competitive advantage, digital marketing, logistics, predictive model, SEM, user engagement, web analytics}, doi = {https://doi.org/10.3390/pr10050892}, url = {https://www.mdpi.com/2227-9717/10/5/892}, author = {Damianos P. Sakas and Dimitrios P. Reklitis and Panagiotis Trivellas and Costas Vassilakis and Marina C. Terzi} } @article {817, title = {Multichannel Digital Marketing Optimizations through Big Data Analytics in the Tourism and Hospitality Industry}, journal = {Journal of Theoretical and Applied Electronic Commerce Research}, volume = {17}, year = {2022}, month = {oct}, pages = {1383{\textendash}1408}, abstract = {

The tourism sector increasingly relies on technology to acquire new clients in a world overflowing with information. So, the main question that needs to be answered is:What digital marketing strategy should be adopted to attract customers and built digital brand name by incorporating websites and social media big data? The authors of this research utilize web analytics and big data to build an innovative methodology in an effort to address this issue. After the data collection, statistical analysis was implemented, followed by a fuzzy cognitive map and an agent-based simulation model in order to illustrate the usage of social media and user experience in multichannel marketing. The findings suggest that, in contrast to the websites of other industries, such as logistics, where customers want to finish their inquiries as quickly as possible and leave the webpage, it is advantageous for tourism websites to keep customers{\textquoteright} attention moreon their website in order to increasevisibility. Additionally, the research further highlights the importance of personalization and user-engagement content to e-WOM, suggesting to tourism businesses to encourage posts made by customers and employees.

}, keywords = {advertising, big data, brand, digital marketing, e-WOM, hospitality, multichannel, social media, tourism, web analytics}, doi = {10.3390/jtaer17040070}, url = {https://www.mdpi.com/0718-1876/17/4/70}, author = {Damianos P. Sakas and Dimitrios P. Reklitis and Marina C. Terzi and Costas Vassilakis} } @conference {812, title = {Persona Finetuning for Online Gaming using Personalisation Techniques}, booktitle = {Proceedings of the 2022 HCII Conference}, year = {2022}, abstract = {

Automatic persona generation has been shown to have specific measurable benefits for application creators and users. In most situations, personas are adequately descriptive and diversified to achieve user type accuracy and coverage. For specific market segments, such as online gaming, using personas may accurately describe existing user base but not changing habit and need that are introduced by the fluidity of the offerings and the delivery methods. Changes in the ways that applications are marketed, such as new payment methods, for example, subscription models, pay-to-play and pay-to-win, payment-driven-gamification, seriously affect user needs and result in direct impact on user acceptance. This work utilises structured user needs from online gaming players to augment personas using personalisation techniques. The personas are finetuned and dediversified to result in concise personas, based on user needs that successfully convey information for creators and users alike.

}, keywords = {collaborative filtering, Data-driven methods, Diversification, Online Gaming, Persona, Personalisation, Usability evaluation, User study}, author = {Dimitris Spiliotopoulos and Dionisis Margaris and Kostas N. Koutrakis and Panos Philippopoulos and Costas Vassilakis} } @article {813, title = {On Producing Accurate Rating Predictions in Sparse Collaborative Filtering Datasets}, journal = {Information}, volume = {13}, year = {2022}, month = {jun}, pages = {302}, abstract = {

The typical goal of a collaborative filtering algorithm is the minimisation of the deviation between rating predictions and factual user ratings so that the recommender system offers suggestions for appropriate items, achieving a higher prediction value. The datasets on which collaborative filtering algorithms are applied vary in terms of sparsity, i.e., regarding the percentage of empty cells in the user{\textendash}item rating matrices. Sparsity is an important factor affecting rating prediction accuracy, since research has proven that collaborative filtering over sparse datasets exhibits a lower accuracy. The present work aims to explore, in a broader context, the factors related to rating prediction accuracy in sparse collaborative filtering datasets, indicating that recommending the items that simply achieve higher prediction values than others, without considering other factors, in some cases, can reduce recommendation accuracy and negatively affect the recommender system{\textquoteright}s success. An extensive evaluation is conducted using sparse collaborative filtering datasets. It is found that the number of near neighbours used for the prediction formulation, the rating average of the user for whom the prediction is generated and the rating average of the item concerning the prediction can indicate, in many cases, whether the rating prediction produced is reliable or not.

}, keywords = {accuracy, collaborative filtering, Evaluation, Personalisation, Rating prediction, Recommender Systems, reliability, Sparse Datasets}, doi = {https://doi.org/10.3390/info13060302}, author = {Dionisis Margaris and Costas Vassilakis and Dimitris Spiliotopoulos} } @article {797, title = {On Addressing the Low Rating Prediction Coverage in Sparse Datasets Using Virtual Ratings}, journal = {SN Computer Science}, volume = {2}, year = {2021}, month = {May}, pages = {255}, abstract = {

Collaborative filtering-based recommendation systems consider users{\textquoteright} likings and interests, articulated as ratings within a database to offer personalized recommendations. Unfortunately, many collaborative filtering datasets exhibit the {\textquoteleft}{\textquoteleft}grey sheep{\textquoteright}{\textquoteright} phenomenon, a state where no near neighbours can be found for certain users. This phenomenon is extremely frequent in datasets where users, on average, have rated only a small percentage of the available items, which are termed as sparse datasets. This paper addresses the {\textquoteleft}{\textquoteleft}grey sheep{\textquoteright}{\textquoteright} problem by proposing the virtual ratings concept and introduces an algorithm for virtual rating creation on the basis of actual ratings. The novelty behind this concept is that the introduction of the virtual ratings effectively reduces the user{\textendash}item rating matrix sparsity, thus alleviating the aforementioned problem. The proposed algorithm, which is termed as CFVR, has been extensively evaluated and the results show that it achieves to considerably improve the capability of a collaborative filtering system to formulate tailored recommendations for each user, when operating on sparse datasets, while at the same time improves rating prediction quality.

}, keywords = {collaborative filtering, Cosine Similarity, Evaluation, Pearson Correlation Coefficient, Recommender Systems, Sparse Datasets, Virtual ratings}, issn = {2661-8907}, doi = {10.1007/s42979-021-00668-8}, url = {https://doi.org/10.1007/s42979-021-00668-8}, author = {Dionisis Margaris and Spiliotopoulos, Dimitris and Karagiorgos, Gregory and Costas Vassilakis and Vasilopoulos, Dionysios} } @article {803, title = {Augmenting Black Sheep Neighbour Importance for Enhancing Rating Prediction Accuracy in Collaborative Filtering}, journal = {Applied Sciences}, volume = {11}, year = {2021}, month = {sep}, pages = {8369}, abstract = {

In this work, an algorithm for enhancing the rating prediction accuracy in collaborative filtering, which does not need any supplementary information, utilising only the users{\textquoteright} ratings on items, is presented. This accuracy enhancement is achieved by augmenting the importance of the opinions of {\textquoteleft}black sheep near neighbours{\textquoteright}, which are pairs of near neighbours with opinion agreement on items that deviates from the dominant community opinion on the same item. The presented work substantiates that the weights of near neighbours can be adjusted, based on the degree to which the target user and the near neighbour deviate from the dominant ratings for each item. This concept can be utilized in various other CF algorithms. The experimental evaluation was conducted on six datasets broadly used in CF research, using two user similarity metrics and two rating prediction error metrics. The results show that the proposed technique increases rating prediction accuracy both when used independently and when combined with other CF algorithms. The proposed algorithm is designed to work without the requirements to utilise any supplementary sources of information, such as user relations in social networks and detailed item descriptions. The aforesaid point out both the efficacy and the applicability of the proposed work.

}, keywords = {black sheep users, collaborative filtering, Evaluation, rating prediction accuracy}, doi = {10.3390/app11188369}, url = {https://doi.org/10.3390/app11188369}, author = {Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @conference {799, title = {Cyber-Security Training Evaluation Metrics}, booktitle = {Proceedings of the 2021 IEEE International Conference on Cyber Security and Resilience}, year = {2021}, publisher = {IEEE}, organization = {IEEE}, abstract = {

Cyber-security training has evolved into an imperative need, aiming to provide cyber-security professionals with the knowledge and skills required to confront cyber-attacks that are increasing in number and sophistication. Training activities are typically associated with evaluation means, aimed to assess the extent to which the trainee has acquired the knowledge and skills whose development is targeted by the training programme, while cyber-security awareness and skill level evaluation means may be used to support additional security-related aspects of organizations. In this paper, we review trainee performance assessment metrics in cyber-security training, aiming to assist designers of cyber-security training activities to identify the mostprominent trainee performance assessment means for their training programmes, while additional research directions involving cyber-security training evaluation metrics are also identified.

}, keywords = {Cyber-ranges, Cyber-security training, Evaluation, Gamification, Scoring}, author = {Koutsouris, Nikolaos and Costas Vassilakis and Kolokotronis, Nicholas} } @article {798, title = {On the Design of IoT Security: Analysis of Software Vulnerabilities for Smart Grids}, journal = {Energies}, volume = {14}, year = {2021}, month = {may}, pages = {2818}, abstract = {

The 5G communication network will underpin a vast number of new and emerging services, paving the way for unprecedented performance and capabilities in mobile networks. In this setting, the Internet of Things (IoT) will proliferate, and IoT devices will be included in many 5G application contexts, including the Smart Grid. Even though 5G technology has been designed by taking security into account, design provisions may be undermined by software-rooted vulnerabilities in IoT devices that allow threat actors to compromise the devices, demote confidentiality, integrity and availability, and even pose risks for the operation of the power grid critical infrastructures. In this paper, we assess the current state of the vulnerabilities in IoT software utilized in smart grid applications from a source code point of view. To that end, we identified and analyzed open-source software that is used in the power grid and the IoT domain that varies in characteristics and functionality, ranging from operating systems to communication protocols, allowing us to obtain a more complete view of the vulnerability landscape. The results of this study can be used in the domain of software development, to enhance the security of produced software, as well as in the domain of automated software testing, targeting improvements to vulnerability detection mechanisms, especially with a focus on the reduction of false positives.

}, keywords = {Internet of Things, robustness, security, software vulnerabilities}, doi = {10.3390/en14102818}, author = {Christos-Minas Mathas and Costas Vassilakis and Nicholas Kolokotronis and Charilaos C. Zarakovitis and Michail-Alexandros Kourtis} } @mastersthesis {848, title = {Development and evaluation of a team formation algorithm for gaming environments}, year = {2021}, month = {10/2021}, pages = {48}, type = {Undergraduate}, abstract = {

In the context of multiplayer online games, but in many other group activities that entail collaboration between user, appropriate group formation is a critical issue. Groups should be formulated in a way that on the one hand user collaboration (or collaboration avoidance) preferences are respected, and on the other hand collaboration potential and productivity of groups is maximized.


In the current thesis, we consider an internet-based collaboration environment, where users work in pairs and, after their collaboration, each of them rates the quality of work and the quality of collaboration of his/her partner. Moreover, users have the option to express a positive, negative or neutral opinion towards the possibility of cooperating with individual users. For such an environment, we have developed an algorithm that employs linear
programming techniques, in order to create an optimal user pair formulation, considering the ratings that users have assigned to other users and collaboration intention statements. We present in detail the system structure, the algorithms and techniques employed, and we analyze the performance of the system in terms of the time needed to formulate user pair assignments
in various indicative cases. Finally, potential future extensions are outlined.

}, keywords = {glpk, Java, linear programming, maximization problem, scpsolver, User groups, μέθοδος simplex method}, author = {Iasonas Topalidis} } @conference {809, title = {Digital applications for the preservation of historic memory: the case of the Kalamata digital museum (greek title: Ψηφιακές εφαρμογές για τη διατήρηση της ιστορικής μνήμης: Η περίπτωση του ψηφιακού μουσείου Καλαμάτας)}, booktitle = {4th PanHellenic Conference on Digital Cultural Heritage-EuroMed 2021}, year = {2021}, abstract = {

The evolution in technology and informatics have changed all aspects of our lives, including civilization-related ones. And while interdisciplinary research involving the scientific disciplines of human sciences and informatics was underdeveloped for many years, it seems that informatics and technology can constitute the catalyst for the rapid advancement of certain areas in human sciences. This has become more than apparent during the last decade, especially in museums and venues related to civilization, where the application of technology, both for the improvement of the visitors{\textquoteright} experience and for the support of scientists (archaeologists, museologists etc), is now taken as granted. In particular, the measures that have been applied during the last two years of the COVID19 pandemic, further accelerate the developments towards digitalization and switching to an online world. The "Kalamata 1821: roads of freedom" project was the starting point for the creation of the first mixed digital museum in the region of the Peloponnese; this museum is strongly related to the history of Greece, starting from the Revolution of 1821 and its relationship with Kalamata. This paper analyses the process of design, preparation and implementation of digital multimedia applications that are installed on the digital museum infrastructure. The applications have been designed to maximize the information that can be perceived within the limited time frame during of a museum visit, offering in parallel means to obtain some of the information presented and store them on a mobile device.

}, author = {Poulopoulos, Vassileios and Wallace, Manolis and Antoniou, Antzela and Costas Vassilakis and Panagiotidi, Vayia and Zacharias, Nikolaos} } @mastersthesis {855, title = {Emotion analysis for videos with Greek speech}, year = {2021}, month = {10/2021}, pages = {44}, type = {Undergraduate}, abstract = {

Opinions play a major role to almost all human activities, because they are key influencers of our choices and way of thinking. Whenever we need to make a decision, we want to know others{\textquoteright} opinions on the subject at hand. In the real world, businesses
and organizations want to know consumer or public opinions about their products and services. On the other hand, individual consumers also want to know the opinions of
other people that have used a particular product, before purchasing it.


With the explosive growth of social networks (e.g. blogs, micro-blogs, forum, reviews, videos, comments and postings in social network sites) on the Web, a huge dataset has
been created, ready to be exploited to find user preferences and opinions. Sentiment analysis focuses on the task of automatically identifying whether a piece of text
expresses a positive or negative polarity about the subject matter. In this thesis, sentiment analysis is performed on Greek review and unboxing videos that are related
to tech products (mostly smartphones and laptops), using a sentiment lexicon. In addition, previous work in this area on Greek and the English languages is examined and compared.

}, author = {Sing Manvir and Costas Vassilakis} } @inbook {796, title = {Handbook of Research on Developing a Post-Pandemic Paradigm for Virtual Technologies in Higher Education}, year = {2021}, publisher = {IGI Global}, organization = {IGI Global}, chapter = {Social Skills and Online Learning}, abstract = {

The concept of online teaching and learning is widely adopted by universities due to the pandemic of COVID-19, which forced them to shift from blending learning (including both direct and remote education) to exclusive online education. Technology has provided a multitude of tools which can prove very useful in the hands of people who want to serve such a great purpose as education. During the days of the pandemic, where people are isolated, virtual community and virtual learning technology brings people together to experience a sense of educational community in the virtual world. This chapter introduces the reader to the importance for social skill training of the learning communities during times that online learning is the sole type of education, exploring methodologies, tools and practices that can be used to counterbalance the deficiencies introduced by distance learning methods regarding social skill development.

}, keywords = {Active learning, Community of Inquiry, COVID-19, Digital Collaboration Platforms, Higher Education, Pandemic, Problem-Based Learning, Remote Learning, Social skills, Virtual Learning Community}, author = {Kriemadis, Athanasios and Kapnisi, Dimitra and Costas Vassilakis and Spiliotopoulos Dimitris} } @inbook {808, title = {Identifying Reliable Recommenders in Users{\textquoteright} Collaborating Filtering and Social Neighbourhoods}, booktitle = {Lecture Notes in Social Networks}, year = {2021}, pages = {51{\textendash}76}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

Recommender systems increasingly use information sourced from social networks to improve the quality of their recommendations. However, both recommender systems and social networks exhibit phenomena under which information for certain users or items is limited, such as the cold start and the grey sheep phenomena in collaborative filtering systems and the isolated users in social networks. In the context of a social network-aware collaborative filtering, where the collaborating filtering- and social network{\textendash}based neighbourhoods are of varying density and utility for recommendation formulation, the ability to identify the most reliable recommenders from each neighbourhood for each user and appropriately combine the information associated with them in the recommendation computation process can significantly improve the quality and accuracy of the recommendations offered. In this chapter, we report on our extensions on earlier works in this area which comprise of (1) the development of an algorithm for discovering the most reliable recommenders of a social network recommender system and (2) the development and evaluation of a new collaborative filtering algorithm that synthesizes the opinions of a user{\textquoteright}s identified recommenders to generate successful recommendations for the particular user. The proposed algorithm introduces significant gains in rating prediction accuracy (4.9\% on average, in terms of prediction MAE reduction and 4.2\% on average, in terms of prediction RMSE reduction) and outperforms other algorithms. The proposed algorithm, by design, utilizes only basic information from the collaborative filtering domain (user{\textendash}item ratings) and the social network domain (user relationships); therefore, it can be easily applied to any social network recommender system dataset.

}, keywords = {collaborative filtering, Evaluation, Limited Information, Near Neighbours, Rating prediction, Recommender Systems, Social Networks}, doi = {10.1007/978-3-030-67044-3_3}, author = {Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @conference {801, title = {An Interface for User-Centred Process and Correlation Between Large Datasets}, booktitle = {Proceedings of the 2021 International Conference on Human-Computer Interaction: Design, User Experience, and Usability: UX Research and Design}, year = {2021}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

Standard database query systems are designed to process data on a single installation only, and do not provide optimal solutions for cases that data from multiple sources need to be queried. In these cases, the sources may have different data schemata, data representations etc., necessitating extensive coding and data transformations to retrieve partial results and combine them to reach the desired outcome. Differences in schemata and representations may be subtle and remain unnoticed, leading to the production of erroneous results. The goal of this paper is to present an easy-to-use solution for the end users, enabling them to query data from a given set of databases through a single user interface. This user interface allows users to visualize database contents and query results, while facilities for uploading and validating the data are also accommodated. To demonstrate the applicability of our approach, a use case is presented where data from two different sources are uploaded into the system and thereafter the data from the two databases can be utilized in tandem. The usability evaluation involved software developers in free evaluation scenarios.

}, keywords = {big data, Multiple data sources, Query, Usability, user interface, Visualisation}, isbn = {978-3-030-78221-4}, doi = {https://doi.org/10.1007/978-3-030-78221-4_32}, author = {Spiliotopoulos, Dimitris and Giannakopoulos, Theodoros and Costas Vassilakis and Wallace, Manolis and Lantzouni, Marina and Poulopoulos, Vassilis and Dionisis Margaris} } @inbook {807, title = {Safe Travelling Period Recommendation to High Attack Risk European Destinations Based on Past Attack Information}, booktitle = {Lecture Notes in Social Networks}, year = {2021}, pages = {77{\textendash}100}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

Terrorism is a significant deterrent for tourism. It affects both visitors and local citizens and personnel of a country or area. On one hand, the potential visitor will probably avoid travelling to a high attack risk country, due to safety reasons, hence will miss the opportunity to visit it, and, on the other hand, the country{\textquoteright}s tourism will decline. This work addresses the aforementioned problem by (1) showing that relatively safe visiting periods for high attack risk European countries can be predicted with high accuracy, using limited information, comprising of attack and fatality data from the past years, which are widely available, and (2) developing an algorithm that recommends relatively safe periods to potential travellers. The results of this work will be useful for tourists, visitors, businesses and operators, as well as relevant stakeholders and actors.

}, keywords = {Evaluation, Recommendation algorithm, Risk Calculation, Safety Perception, Safety prediction, Terrorist Attacks, tourism}, doi = {10.1007/978-3-030-67044-3_3}, author = {Dimitris Spiliotopoulos and Dionisis Margaris and Costas Vassilakis} } @conference {800, title = {Understanding and mitigating banking trojans: From Zeus to Emotet}, booktitle = {Proceedings of the 2021 IEEE International Conference on Cyber Security and Resilience}, year = {2021}, publisher = {IEEE}, organization = {IEEE}, abstract = {

Banking Trojans came a long way in the past decade, and the recent case of Emotet showed their enduring relevance. The evolution of the modern computing landscape can be traced through Emotet and Zeus, both representative examples from the end of the past decade. As an example of earlier malware, Zeus only needed to employ simple anti-analysis techniques to stay undetected; while the more recent Emotet had to constantly evolve to stay a step ahead. Current host-based antimalware solutions face an increasing number of obstacles to perform their function. A multi-layer approach to network security is necessary for network-based intrusion response systems to secure modern networks of heterogeneous devices. A system based on a combination of a graphical network security model and a game theoretic model of cyber attacks was tested on a testbed with Windows machines infected with Trojans; experimental results showed that the proposed system effectively blocked Trojans{\textquoteright} network communications effectively preventing data leakage and yielding encouraging results for future work.

}, keywords = {Cyber security, Graphical security models, Intrusion response systems, Malware analysis, Reverse engineering}, author = {Grammatikakis, Konstantinos-Panagiotis and Koufos, Ioannis and Kolokotronis, Nicholas and Costas Vassilakis and Shiaeles, Stavros} } @conference {802, title = {A User Interface for Personalising WS-BPEL Scenarios}, booktitle = {Proceedings of the 2021 International Conference on Human-Computer Interaction: HCI in Business, Government and Organizations}, year = {2021}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

Due to the huge volume of web services available, both locally and in the cloud, the performance of users and systems need significant research attention. Since WS-BPEL is the dominant language for orchestrating individual web services into business processes, by composing WS-BPEL scripts/scenarios, graphical notations facilitating WS-BPEL design can be extremely useful. Current user interfaces allow WS-BPEL designers not only to invoke selected web services, but also to explicitly ask for recommendations. Then, the user interface appends the services achieving the highest score, according to the attributes{\textquoteright} importance, set by the designer, to their WS-BPEL scenario. However, since the final selection is produced automatically, rather than relying on the designers{\textquoteright} choices, many times, from a personalisation point of view, the adaptation fails. This work reports on the design, development and user evaluation of a user interface that incorporates functionalities that support the designers{\textquoteright} selection performance, thereby upgrading the personalisation level of the WS-BPEL scenarios, as well as the success of the adaptation.

}, keywords = {Personalisation, Recommender Systems, Usability, User evaluation, user interface, Web services, WS-BPEL scenarios}, isbn = {978-3-030-77750-0}, doi = {https://doi.org/10.1007/978-3-030-77750-0_25}, author = {Dionisis Margaris and Spiliotopoulos, Dimitris and Vasilopoulos, Dionysios and Costas Vassilakis} } @article {771, title = {An Adaptive Social Network-Aware Collaborative Filtering Algorithm for Improved Rating Prediction Accuracy}, journal = {IEEE Access}, volume = {8}, year = {2020}, pages = {68301{\textendash}68310}, abstract = {When information from traditional recommender systems is augmented with information about user relationships that social networks store, more successful recommendations can be produced. However, this information regarding user relationships may not always be available, since some users may not consent to the use of their social network information for recommendations or may not have social network accounts at all. Moreover, the rating data (categories and characteristics of products) may be unavailable for a recommender system. In this paper, we present an algorithm that can be applied in any social network-aware recommender system that utilizes the users{\textquoteright} ratings on items and users{\textquoteright} social relations. The proposed algorithm addresses the issues of limited social network information or limited collaborative filtering information for some users by adapting its behavior, taking into account the density and utility of each user{\textquoteright}s social network and collaborative filtering neighborhoods. Through this adaptation, the proposed algorithm achieves considerable improvement in rating prediction accuracy. Furthermore, the proposed algorithm can be easily implemented in recommender systems}, keywords = {Performance evaluation, Recommender Systems, Social computing}, issn = {2169-3536}, doi = {10.1109/access.2020.2981567}, author = {Dionisis Margaris and Anna Kobusinska and Dimitris Spiliotopoulos and Costas Vassilakis} } @article {779, title = {An Algorithm for Density Enrichment of Sparse Collaborative Filtering Datasets Using Robust Predictions as Derived Ratings}, journal = {Algorithms}, volume = {13}, year = {2020}, month = {07/2020}, pages = {174}, abstract = {

Collaborative filtering algorithms formulate personalized recommendations for a user, first by analysing already entered ratings to identify other users with similar tastes to the user (termed as near neighbours), and then using the opinions of the near neighbours to predict which items the target user would like. However, in sparse datasets, too few near neighbours can be identified, resulting in low accuracy predictions and even a total inability to formulate personalized predictions. This paper addresses the sparsity problem by presenting an algorithm that uses robust predictions, that is predictions deemed as highly probable to be accurate, as derived ratings. Thus, the density of sparse datasets increases, and improved rating prediction coverage and accuracy are achieved. The proposed algorithm, termed as CFDR, is extensively evaluated using (1) seven widely-used collaborative filtering datasets, (2) the two most widely-used correlation metrics in collaborative filtering research, namely the Pearson correlation coefficient and the cosine similarity, and (3) the two most widely-used error metrics in collaborative filtering, namely the mean absolute error and the root mean square error. The evaluation results show that, by successfully increasing the density of the datasets, the capacity of collaborative filtering systems to formulate personalized and accurate recommendations is considerably improved.

}, keywords = {collaborative filtering, density enrichment, derived ratings, rating prediction accuracy, rating prediction coverage, Recommender Systems, robust predictions, Sparse Datasets}, doi = {https://doi.org/10.3390/a13070174}, author = {Dionisis Margaris and Dimitris Spiliotopoulos and Gregory Karagiorgos and Costas Vassilakis} } @article {776, title = {Application cases of the Additional Testsuites Framework}, year = {2020}, abstract = {

The Additional Testsuites Framework is a novel test suite management approach, which allows for holistic management of test suites for any software program. In particular, the tests can be maintained in a centralized repository, and are expanded and maintained independently of specific versions of the associated program. Through the use of annotations, tests are categorized and distributed to the desired versions of the software program. Currently, the Additional Testsuites Framework concept has been implemented and successfully used for testing a number of real-world software programs, notably including the JBoss Server. The presented framework also supports test-based development, while it can also support additional functionalities, such as dynamic/selective program builds. In this report, we provide a list of notable cases where the AT Framework has been applied on real-world software programs.

}, author = {Panagiotis Sotiropoulos and Costas Vassilakis} } @article {782, title = {Data-Assisted Persona Construction Using Social Media Data}, journal = {Big Data and Cognitive Computing}, volume = {4}, year = {2020}, month = {aug}, pages = {21}, abstract = {

User experience design and subsequent usability evaluation can benefit from knowledge about user interaction, types, deployment settings and situations. Most of the time, the user type and generic requirements are given or can be obtained and used to model interaction during the design phase. The deployment settings and situations can be collected through the needfinding phase, either via user feedback or via the automatic analysis of existing data. Personas may be defined using the aforementioned information through user research analysis or data analysis. This work utilizes an approach to activate an accurate persona definition early in the design cycle, using topic detection to semantically enrich the data that are used to derive the persona details. This work uses Twitter data from a music event to extract information that can be used to assist persona creation. A user study in persona construction compares the topic modelling metadata to a traditional user collected data analysis for persona construction. The results show that the topic information-driven constructed personas are perceived as having better clarity, completeness and credibility. Additionally, the human users feel more attracted and similar to such personas. This work may be used to model personas and recommend suitable ones to designers of other products, such as advertisers, game designers and moviegoers.

}, keywords = {Cultural Events, Persona, personalization, Topic Modelling, Usability, User Experience, User Interface Design}, doi = {10.3390/bdcc4030021}, author = {Dimitris Spiliotopoulos and Dionisis Margaris and Costas Vassilakis} } @article {721, title = {Detection of intermittent faults in software programs through identification of suspicious shared variable access patterns}, journal = {Journal of Systems and Software}, volume = {159}, year = {2020}, month = {30 October 2019}, pages = {110455}, abstract = {Intermittent faults are a very common problem in the software world, while difficult to be debugged. Most of the existing approaches though assume that suitable instrumentation has been provided in the program, typically in the form of assertions that dictate which program states are considered to be erroneous. In this paper we propose a method that can be used to detect probable sources of intermittent faults within a program. Our method proposes certain points in the code, whose data interdependencies combined with their execution interweaving indicate that they could be the cause of intermittent faults. It is the responsibility of the user to accept or reject these proposals. An advantage of this method is that it removes the need for having predefined assertion points in the code, being able to detect potential sources of intermittent faults in the whole bulk of the code, with no instrumentation requirements on the side of the programmer. The proposed approach exploits information from the dynamic behavior of the program. In comparison with parser-based approaches which analyze only the program structure, our approach is immutable to language term changes and in general is not depending on any user-provided assertions or configuration.}, keywords = {Fault detection, Intermittent faults, Model-based checking, Shared variables}, issn = {0164-1212}, doi = {10.1016/j.jss.2019.110455}, author = {Panagiotis Sotiropoulos and Costas Vassilakis} } @article {788, title = {Examining the use of STEAM Education in Preschool Education}, journal = {European Journal of Engineering Research and Science}, volume = {TBD}, year = {2020}, month = {TBD}, abstract = {

STEAM (Science, Technology, Engineering, Arts and Mathematics) initiatives are of current interest for both in-school and out-of-school contexts in North America. This is a new concept which is shifting educational paradigms towards art integration in STEM subjects. This article focuses on the need for STEAM education at the early childhood level and investigates the teaching and educational models of STEAM education in the kindergarten and in the first grades of primary school and how pre-school and primary school teachers see these models in the Greek context but also what students eventually learn from these models. The purpose of this chapter is to better understand the educational programs of STEAM education, which are offered by non-profit organizations and both public and private schools. Preschool children have a natural disposition toward science with their sense of curiosity and creativity. More research needs to be done in the area of STEAM implementation in the K-8 classrooms to incorporate engineering education.

}, keywords = {Early science education, Greek STEAM implementation, K-8 STEAM, STEAM educational models, STEM/STEAM education}, author = {C. Spyropoulou and M. Wallace and Costas Vassilakis and V. Poulopoulos} } @conference {lykourentzou_2019_crops, title = {Exploring Self-organisation in Crowd Teams}, booktitle = {Proceedings of the Crowd-Powered e-Services (CROPS) Workshop in the context of the 19th IFIP Conference on e-Business, e-Services and e-Society (I3E 2019)}, year = {2020}, month = {01/2020}, abstract = {

Online crowds have the potential to do more complex work in teams, rather than as individuals. Team formation algorithms typically maximize some notion of global utility of team output by allocating people to teams or tasks. However, decisions made by these algorithms do not consider the decisions or preferences of the people themselves. This paper explores a complementary strategy, which relies on the crowd itself to self-organize into eective teams. Our preliminary results show that users perceive the ability to choose their teammate extremely useful in a crowdsourcing setting. We also nd that self-organisation makes users feel more productive, creative and responsible for their work product.

}, keywords = {computer-supported collaboration, creative writing, crowd teams, self-organization}, doi = {10.1007/978-3-030-39634-3_15}, author = {Ioanna Lykourentzou and Antonios Liapis and Costas Papastathis and Konstantinos Papangelis and Costas Vassilakis} } @article {723, title = {A Fine-grained Social Network Recommender System}, journal = {Social Network Analysis and Mining}, volume = {10}, year = {2020}, abstract = {Recommender systems have greatly evolved in recent years and have become an integral part of the Web. From e-commerce sites to mobile apps, our daily routine revolves around a series of {\textquotedblleft}small{\textquotedblright} decisions that are influenced by such recommendations. In a similar manner, online social networks recommend only a subset of the massive amount of content published by a user{\textquoteright}s friends. However, the prevalent approach for the content selection process in such systems is driven by the amount of interaction between the user and the friend who published the content. As a result, content of interest is often lost due to weak social ties. In this paper, we present a fine-grained recommender system for social ecosystems, designed to recommend media content (e.g., music videos, online clips) published by the user{\textquoteright}s friends. The system design was driven by the findings of our qualitative user study that explored the value and requirements of a recommendation component within a social network. The core idea behind the proposed approach was to leverage the abundance of preexisting information in each user{\textquoteright}s account for creating interest profiles, to calculate similarity scores at a fine-grained level for each friend. The intuition behind the proposed method was to find consistent ways to obtain information representations that can identify overlapping interests in very specific sub-categories (e.g., two users{\textquoteright} music preferences may only coincide on hard rock). While the system is intended as a component of the social networking service, we developed a proof-of-concept implementation for Facebook and explored the effectiveness of our underlying mechanisms for content analysis. Our experimental evaluation demonstrates the effectiveness of our approach, as the recommended content of interest was both overlooked by the existing Facebook engine and not contained in the users{\textquoteright} Facebook News Feed. We also conducted a user study for exploring the usability aspects of the prototype and found that it offers functionality that could significantly improve user experience in popular services.}, keywords = {Content Analysis, Interest Profiles, Recommender Systems, Social Networks, Usability}, issn = {1869-5469}, doi = {10.1007/s13278-019-0621-7}, author = {Markos Aivazoglou and Antonios Roussos and Dionisis Margaris and Costas Vassilakis and Sotiris Ioannidis and Jason Polakis and Dimitris Spiliotopoulos} } @conference {795, title = {From Smart Cities to Smart Rural Country: challenges and sustainability}, booktitle = {Extended abstract Presentation in the 15th National and International Conderence of the Hellenic Society for Systemic Studies}, year = {2020}, abstract = {

This work presents the current progress on smart cities initiatives, major breakthroughs and challenges. It also reviews the smart villages and smart rural environments as the next evolution of the smart cities vision. The purpose of the Smart Cities Mission is to drive economic growth and improve the quality of life of people by enabling local area development and harnessing technology, especially technology that leads to Smart outcomes. Technologies such as IoT (sensors, networks and applications) can be leveraged to improve city services, utilities, the environment and quality of life. All technologies have a common base, big data. Relevant data are collected by local sensors, such as citizens and local activities and global sensors, such as the environment, financial institutions and government sources. Data from disparate sources (traffic, air/water quality and usage, energy usage, resident movement) is constantly collected and is available for analysis The aim is to use the already gained expertise and insights from the smart cities approaches, applications and evaluations as well as the early works on smart villages and rural spaces to formulate the challenges and sustainability goals for the smart rural country. The findings of this work are mostly applied to medium- and long-term challenges as well as toward the notion of smart communities. Smart communities represent the notion of abstract connected objects within or spanning smart urban and rural spaces, such as smart cultural heritage, smart environment, and others. Introducing the non-technical goals for smart communities provides the sense of purpose and tangible targets for the technical-oriented smart urban and rural approaches, for aspiration and sustainability planning for the future.

}, author = {Dimitris Spiliotopoulos and Athanasios Kriemadis and Costas Vassilakis} } @article {749, title = {Human behaviour in multimodal interaction: main effects of civic action and interpersonal and problem-solving skills}, journal = {Journal of Ambient Intelligence and Humanized Computing}, volume = {TBD}, year = {2020}, month = {mar}, pages = {TBD}, abstract = {Metacognitive skill training may rest within any kind of social interaction that requires awareness of what an individual and others think, in social, educational and organizational settings alike. This work explores an extensive study of multimodal application interaction (virtual agent, spoken dialogue, visual communication of progress) for metacognitive skill training via negotiation skill training settings. Human behaviour, as effected by civic action and interpersonal and problem-solving skill training, is investigated through interaction sessions with a virtual agent on multimodal multiparty negotiation. This work reports on the results of the user-system evaluation sessions involving 41 participants before-and-after interaction with the system, integrating macro- (dialogue system performance) and micro- (metacognitive-related and individual-and-community level-related attitudes and skills) factors. Findings indicate significant and positive relationships between user and system evaluation questions after interaction with the dialogue system and between self-efficacy, self-regulation, individual readiness to change, mastery goal orientation, interpersonal and problem-solving skills and civic action before-and-after the interaction experience. Implications, limitations and further research issues are discussed in light of context of the multimodal interaction and its effects on the human behaviour during metacognitive skill training.}, keywords = {Human Behaviour, Individual- and Community-Level Related Attitudes and Skills, Metacognitive, Multimodal Interaction, Skill Training}, doi = {10.1007/s12652-020-01846-x}, author = {Markri, Eleni and Spiliotopoulos, Dimitris and Costas Vassilakis and Dionisis Margaris} } @article {772, title = {Hydria: An Online Data Lake for Multi-Faceted Analytics in the Cultural Heritage Domain}, journal = {Big Data and Cognitive Computing}, volume = {4}, year = {2020}, pages = {7}, abstract = {Advancements in cultural informatics have significantly influenced the way we perceive, analyze, communicate and understand culture. New data sources, such as social media, digitized cultural content, and Internet of Things (IoT) devices, have allowed us to enrich and customize the cultural experience, but at the same time have created an avalanche of new data that needs to be stored and appropriately managed in order to be of value. Although data management plays a central role in driving forward the cultural heritage domain, the solutions applied so far are fragmented, physically distributed, require specialized IT knowledge to deploy, and entail significant IT experience to operate even for trivial tasks. In this work, we present Hydria, an online data lake that allows users without any IT background to harvest, store, organize, analyze and share heterogeneous, multi-faceted cultural heritage data. Hydria provides a zero-administration, zero-cost, integrated framework that enables researchers, museum curators and other stakeholders within the cultural heritage domain to easily (i) deploy data acquisition services (like social media scrapers, focused web crawlers, dataset imports, questionnaire forms), (ii) design and manage versatile customizable data stores, (iii) share whole datasets or horizontal/vertical data shards with other stakeholders, (iv) search, filter and analyze data via an expressive yet simple-to-use graphical query engine and visualization tools, and (v) perform user management and access control operations on the stored data. To the best of our knowledge, this is the first solution in the literature that focuses on collecting, managing, analyzing, and sharing diverse, multi-faceted data in the cultural heritage domain and targets users without an IT background.}, keywords = {analytics and visualization, big data management, Cultural heritage, data lake, data store, open source}, doi = {10.3390/bdcc4020007}, url = {https://www.mdpi.com/2504-2289/4/2/7}, author = {Kimon Deligiannis and Paraskevi Raftopoulou and Christos Tryfonopoulos and Nikos Platis and Costas Vassilakis} } @article {margaris-IJBDI-2019-b, title = {Improving collaborative filtering{\textquoteright}s rating prediction accuracy by considering users{\textquoteright} dynamic rating variability}, journal = {International Journal of Big Data Intelligence}, volume = {7}, year = {2020}, chapter = {59--71}, abstract = {

Users that populate ratings databases, follow different marking practices, in the sense that some are stricter, while others are more lenient. Similarly, users{\textquoteright} rating practices may also differ in rating variability, in the sense that some users may be entering ratings close to their mean, while other users may be entering more extreme ratings, close to the limits of the rating scale. While this aspect has been recently addressed through the computation and exploitation of an overall rating variability measure per user, the fact that user rating practices may vary along the user{\textquoteright}s rating history time axis may render the use of the overall rating variability measure inappropriate for performing the rating prediction adjustment. In this work, we (1) propose an algorithm that considers two variability metrics per user, the global (overall) and the local one, with the latter representing the user{\textquoteright}s variability at prediction time, (2) present alternative methods for computing a user{\textquoteright}s local variability and (3) evaluate the performance of the proposed algorithm in terms of rating prediction quality and compare it against the state-of-the-art algorithm that employs a single variability metric in the rating prediction computation process.

}, keywords = {collaborative filtering, Cosine Similarity, Evaluation, Pearson Correlation Coefficient, prediction accuracy, users{\textquoteright} ratings dynamic variability}, doi = {10.1504/ijbdi.2020.107373}, author = {Dionisis Margaris and Costas Vassilakis} } @article {margaris-IJBDI-2019-a, title = {Improving collaborative filtering{\textquoteright}s rating prediction coverage in sparse datasets by exploiting the {\textquotedblleft}friend of a friend{\textquotedblright} concept}, journal = {International Journal of Big Data Intelligence}, volume = {7}, year = {2020}, chapter = {47}, abstract = {

Collaborative filtering computes personalized recommendations by taking into account ratings expressed by users. Collaborative filtering algorithms firstly identify people having similar tastes, by examining the likeness of already entered ratings. Users with highly similar tastes are termed {\textquotedblleft}near neighbours{\textquotedblright} and recommendations for a user are based on her near neighbours{\textquoteright} ratings. However, for a number of users no near neighbours can be found, a problem termed as the {\textquotedblleft}gray sheep{\textquotedblright} problem. This problem is more intense in sparse datasets, i.e. datasets with relatively small number of ratings, compared to the number of users and items. In this work, we propose an algorithm for alleviating this problem by exploiting the friend of a friend (FOAF) concept. The proposed algorithm, CFfoaf, has been evaluated against eight widely used sparse datasets and under two widely used collaborative filtering correlation metrics, namely the Pearson Correlation Coefficient and the Cosine Similarity and has been proven to be particularly effective in increasing the percentage of users for which personalized recommendations can be formulated in the context of sparse datasets, while at the same time improving rating prediction quality.

}, keywords = {collaborative filtering, Cosine Similarity, Evaluation, friend-of-a-friend, Pearson Correlation Coefficient, prediction accuracy, Recommender Systems, Sparse Datasets}, issn = {2053-1389}, doi = {10.1504/ijbdi.2020.106178}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {784, title = {MOOC Accessibility from the Educator Perspective}, booktitle = {Proceedings of the 22nd International Conference on Human-Computer Interaction}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

This work presents the universal access design principles and methods for natural language communication design in e-learning for the disabled. It unfolds a theoretical perspective to the design-for-all methodology and provides a framework description for technologies for creating accessible content for educational content communication. Main concerns include the problem identification of design issues for universal accessibility of spoken material, the primary pedagogical aspects that such content implementation should follow upon, as well as look into the state of the most popular e-learning platforms for which educators create and communicate educational content in an e-learning environment. References to massive open online course platform types of content that exist at the moment are examined in order to understand the challenges of bridging the gap between the modern design of rich courses and universal accessibility. The paper looks into the existing technologies for accessibility and a frame for analysis, including methodological and design issues, available resources and implementation using the existing technologies for accessibility and the perception of the designer as well as the user standpoint. Finally, a study to inform and access how potential educators may perceive the accessibility factor shows that accessible content is a major requirement toward a successful path to universally accessible e-learning.

}, keywords = {design-for-all, interactive e-learning, MOOC, speech processing, technologies for accessibility, universal accessibility}, url = {10.1007/978-3-030-60149-2_10}, author = {Dimitris Spiliotopoulos and Vassilis Poulopoulos and Dionisis Margaris and Eleni Makri and Costas Vassilakis} } @article {781, title = {Multimodal Interaction: Correlates of Learners{\textquoteright} Metacognitive Skill Training Negotiation Experience}, journal = {Information}, volume = {11}, year = {2020}, month = {jul}, pages = {381}, abstract = {

Metacognitive training reflects knowledge, consideration and control over decision-making and task performance evident in any social and learning context. Interest in understanding the best account of effective (win-win) negotiation emerges in different social and cultural interactions worldwide. The research presented in this paper explores an extended study of metacognitive training system during negotiation using an embodied conversational agent. It elaborates on the findings from the usability evaluation employing 40 adult learners pre- and postinteraction with the system, reporting on the usability and metacognitive, individual- and community-level related attributes. Empirical evidence indicates (a) higher levels of self-efficacy, individual readiness to change and civic action after user-system experience, (b) significant and positive direct associations between self-efficacy, self-regulation, interpersonal and problem-solving skills, individual readiness to change, mastery goal orientation and civic action pre- and postinteraction and (c) gender differences in the perceptions of system usability performance according to country of origin. Theoretical and practical implications in tandem with future research avenues are discussed in light of embodied conversational agent metacognitive training in negotiation.

}, keywords = {big data, Cultural Events, Persona, personalization, Topic Modelling, Usability, User Experience, User Interface Design}, doi = {10.3390/info11080381}, author = {Dimitris Spiliotopoulos and Eleni Makri and Costas Vassilakis and Dionisis Margaris} } @conference {786, title = {Policy Making Analysis and Practitioner User Experience}, booktitle = {Proceedings of the 22nd International Conference on Human-Computer Interaction}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

This article presents the work on social media analysis-driven policy-making platforms that are powered by classic social media analysis technologies, such as policy modelling, linguistic analysis, opinion mining, sentiment analysis and information visualization. The approach examines the user design perspective towards user experience in policymaking for all the innovative modules used. The technology behind such complex task is presented while the resulting platform is appraised on the potential for real world application. The findings drive the development and the requirements for the summative usability assessment tests. We also report on the level the practitioners adopted the policy formulation tools.

}, keywords = {Content Analysis, natural language interfaces, opinion mining, policy making, social network analysis, User Experience}, doi = {10.1007/978-3-030-60114-0_29}, author = {Dimitris Koryzis and Fotios Fitsilis and Dimitris Spiliotopoulos and Theocharis Theocharopoulos and Dionisis Margaris and Costas Vassilakis} } @inbook {780, title = {Reconnaisance}, booktitle = {Cyber-Security Threats, Actors, and Dynamic Mitigation}, year = {2020}, publisher = {CRC Press}, organization = {CRC Press}, abstract = {

Reconnaissance is the phase of gathering information about an organization{\textquoteright}s network and computing devices. This information includes both technical characteristics, such as IP addresses and software, and non-technical aspects, such as people operating the devices and the business value of tangible or intangible assets associated with the computing infrastructure. This information allows attackers to better understand their target and prepare elaborate attack plans. The reconnaissance phase is itself divided in a number of subphases, and each subphase is supported by a multitude of tools. In this chapter, we firstly describe in more detail the reconnaissance phase, while subsequently we present the different subphases and the methods and tools supporting each one, providing specific examples of how reconnaissance actions are performed. The information presented in this chapter can be used by organizations{\textquoteright} cyber-security officers to identify weaknesses in the organizations{\textquoteright} security plan implementations and take appropriate mitigation measures.

}, keywords = {Actors, Cyber-Security Threats, Dynamic Mitigation, Reconnaissance}, author = {Mathas, Christos-Minas and Costas Vassilakis}, editor = {Nicholas Kolokotronis and Stavros Shiaeles} } @article {770, title = {A Semantic Mixed Reality Framework for Shared Cultural Experiences Ecosystems}, journal = {Big Data and Cognitive Computing}, volume = {4}, year = {2020}, month = {4/2020}, pages = {6}, abstract = {This paper presents SemMR, a semantic framework for modelling interactions between human and non-human entities and managing reusable and optimized cultural experiences, towards a shared cultural experience ecosystem that might seamlessly accommodate mixed reality experiences. The SemMR framework synthesizes and integrates interaction data into semantically rich reusable structures and facilitates the interaction between different types of entities in a symbiotic way, within a large, virtual, and fully experiential open world, promoting experience sharing at the user level, as well as data/application interoperability and low-effort implementation at the software engineering level. The proposed semantic framework introduces methods for low-effort implementation and the deployment of open and reusable cultural content, applications, and tools, around the concept of cultural experience as a semantic trajectory or simply, experience as a trajectory (eX-trajectory). The methods facilitate the collection and analysis of data regarding the behaviour of users and their interaction with other users and the environment, towards optimizing eX-trajectories via reconfiguration. The SemMR framework supports the synthesis, enhancement, and recommendation of highly complex reconfigurable eX-trajectories, while using semantically integrated disparate and heterogeneous related data. Overall, this work aims to semantically manage interactions and experiences through the eX-trajectory concept, towards delivering enriched cultural experiences.}, keywords = {cultural experience, intelligent interaction, Mixed Reality, semantics, Usability}, doi = {https://doi.org/10.3390/bdcc4020006}, author = {Costas Vassilakis and Konstantinos Kotis and Dimitris Spiliotopoulos and Dionisis Margaris and Vlasios Kasapakis and Christos-Nikolaos Anagnostopoulos and Georgios Santipantakis and George A. Vouros and Theodore Kotsilieris and Volha Petukhova and Andrei Malchanau and Ioanna Lykourentzou and Kaj Michael Helin and Artem Revenko and Nenad Gligoric and Boris Pokric} } @conference {777, title = {Semantics-Driven Conversational Interfaces for Museum Chatbots}, booktitle = {Proceedings of the 22nd International Conference on Human-Computer Interaction, volume "Culture and Computing"}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

This work addresses the challenges of creating usable and personalized conversational interfaces for broad, yet applicable, domains that require user engagement and learning, such as museum chatbots. Whether the chatbots are standalone or coupled with virtual agents or real-life robots, the functional requirements for interaction that targets specific learning aspects would be expected to be more or less similar. This work reports on experimental semantics-driven conversational interface design for chatbots in museum settings, targeting visitors to converse about exhibits and learn information about their style, the artists, the era, and other aspects related to them. Depending on the semantics (presentation, learning, exploration), chatbot scenarios were designed and evaluated by participants in a formative evaluation. The evaluation show that user requirement perception manifests in expectations on the semantic level, instead of just the technical level. The results between the scenarios are compared to see how the semantics considered for the design transferred to the implementation and to the user perception.

}, keywords = {chatbots, conversational interfaces, cultural technology, semantics}, doi = {10.1007/978-3-030-50267-6_20}, author = {Dimitris Spiliotopoulos and Konstantinos Kotis and Costas Vassilakis and Dionisis Margaris} } @conference {778, title = {{\textquotedblleft}Talking{\textquotedblright} Triples to Museum Chatbots}, booktitle = {Proceedings of the 22nd International Conference on Human-Computer Interaction, volume "Culture and Computing"}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

The paper presents recent work on the design and development of AI chatbots for museums using Knowledge Graphs (KGs). The utilization of KGs as a key technology for implementing chatbots raises not only issues related to the representation and structuring of exhibits{\textquoteright} knowledge in suitable formalism and models, but also issues related to the translation of natural language dialogues to and from the selected technology for the formal representation and structuring of information and knowledge. Moreover, such a translation must be as transparent as possible to visitors, towards a realistic human-like question-answering process. The paper reviews and evaluates a number of recent approaches for the use of KGs in developing AI chatbots, as well as key tools that provide solutions for natural language translation and the querying of Knowledge Bases and Linked Open Data sources. This evaluation aims to provide answers to issues that are identified within the proposed MuBot approach for designing and implementing AI chatbots for museums. The paper also presents Cretan MuBot, the first experimental KG/Ontology-based AI chatbot of the MuBot Platform, which is under development in the Heracleum Archaeological Museum.

}, keywords = {chatbots, knowledge graphs, Museums, NLP, RDF triples}, doi = {10.1007/978-3-030-50267-6_22}, author = {Savvas Varitimiadis and Konstantinos Kotis and Dimitris Spiliotopoulos and Costas Vassilakis and Dionisis Margaris} } @conference {783, title = {Threat landscape for smart grid systems}, booktitle = {Proceedings of the 15th International Conference on Availability, Reliability and Security}, year = {2020}, month = {jul}, publisher = {ACM}, organization = {ACM}, abstract = {

Smart Grids are energy delivery networks, constituting an evolution of power grids, in which a bidirectional flow between power providers and consumers is established. These flows support the transfer of electricity and information, in order to support automation actions in the context of the energy delivery network. Insofar, many smart grid implementations and implementation proposals have emerged, with varying degrees of feature delivery and sophistication. While smart grids offer many advantages, their distributed nature and information flow streams between energy producers and consumers enable the launching of a number of attacks against the smart grid infrastructure, where the related consequences may range from economic loss to complete failure of the smart grid. In this paper, we survey the threat landscape of smart grids, identifying threats that are specific to this infrastructure, providing an assessment of the severity of the consequences of each attack type, discerning features that can be utilized to detect attacks and listing methods that can be used to mitigate them.

}, keywords = {attack detection features, attack mitigation, attacks, security, Smart grids}, doi = {https://doi.org/10.1145/3407023.3409229}, author = {Christos-Minas Mathas and Konstantinos-Panagiotis Grammatikakis and Costas Vassilakis and Nicholas Kolokotronis and Vasiliki-Georgia Bilali and Dimitris Kavallieros} } @conference {789, title = {A Trust Management System for the IoT domain}, booktitle = {Proceedings the 2020 IEEE World Congress on Services (SERVICES)}, year = {2020}, publisher = {IEEE}, organization = {IEEE}, abstract = {

In modern internet-scale computing, interaction between a large number of parties that are not known a-priori is predominant, with each party functioning both as a provider and consumer of services and information. In such an environment, traditional access control mechanisms face considerable limitations, since granting appropriate authorizations to each distinct party is infeasible both due to the high number of grantees and the dynamic nature of interactions. Trust management has emerged as a solution to this issue, offering aids towards the automated verification of actions against security policies. In this paper, we present a trust- and risk-based approach to security, which considers status, behavior and associated risk aspects in the trust computation process, while additionally it captures user-to-user trust relationships which are propagated to the device level, through user-to-device ownership links.

}, keywords = {associated risk, behavior, Internet-of-things, status, trust management}, doi = {10.1109/SERVICES48979.2020.00047}, author = {Christos-Minas Mathas and Costas Vassilakis and Nicholas Kolokotronis} } @conference {785, title = {A User Interface for Personalized Web Service Selection in Business Processes}, booktitle = {Lecture Notes in Computer Science}, year = {2020}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {

Nowadays, due to the huge volume of information available on the web, the need for personalization is more than necessary. Choosing the right information for each user is as important as the way this information is presented to him or her. Currently, user-triggered recommendation requests for web services are implemented as an automatic recommendation based on parametric computation. This work reports on a specialized user interface for business processes, where writing code entails invocation of business process information. The paper presents the user interface design for Personalized Web Service Selection in Business Process scenario execution and the user evaluation by business process engineers.

}, keywords = {adaptation, business processes, personalization, user interface, Web services, WS-BPEL}, doi = {10.1007/978-3-030-60152-2_41}, author = {Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis and Gregory Karagiorgos} } @article {787, title = {Visualizing the educational data mining literature}, journal = {European Journal of Engineering Research and Science}, volume = {TBD}, year = {2020}, month = {TBD}, abstract = {

This article provides a visualization of a literature review in students{\textquoteright} performance prediction using educational data mining (EDM) techniques for the period 2015-2019. The results of the review are presented concisely and simply with the use of diagrams. Various aspects of the literature are examined, such as the algorithms adopted, the type of results drawn, the educational setting of the application and the actual exploitation of the outcomes. Findings indicate that tertiary education dominates the EDM field; in contrast, the focus given to secondary and primary education is minimal.

}, keywords = {Educational Data Mining, Literature review, Student Performance, Visualization}, author = {I. Papadogiannis and N. Platis and V. Poulopoulos and Costas Vassilakis and G. Lepouras and M. Wallace and G. Karountzou} } @article {775, title = {What makes a review a reliable rating in recommender systems?}, journal = {Information Processing \& Management}, volume = {57}, year = {2020}, month = {04/2020}, pages = {102304}, abstract = {

The way that users provide feedback on items regarding their satisfaction varies among systems: in some systems, only explicit ratings can be entered; in other systems textual reviews are accepted; and in some systems, both feedback types are accommodated. Recommender systems can readily exploit explicit ratings in the rating prediction and recommendation formulation process, however textual reviews -which in the context of many social networks are in abundance and significantly outnumber numeric ratings- need to be converted to numeric ratings. While numerous approaches exist that calculate a user{\textquoteright}s rating based on the respective textual review, all such approaches may introduce errors, in the sense that the process of rating calculation based on textual reviews involves an uncertainty level, due to the characteristics of the human language, and therefore the calculated ratings may not accurately reflect the actual ratings that the corresponding user would enter. In this work (1) we examine the features of textual reviews, which affect the reliability of the review-to-rating conversion procedure, (2) we compute a confidence level for each rating, which reflects the uncertainty level for each conversion process, (3) we exploit this metric both in the users{\textquoteright} similarity computation and in the prediction formulation phases in recommender systems, by presenting a novel rating prediction algorithm and (4) we validate the accuracy of the presented algorithm in terms of (i) rating prediction accuracy, using widely-used recommender systems datasets and (ii) recommendations generated for social network user satisfaction and precision, where textual reviews are abundant.

}, keywords = {collaborative filtering, Confidence level, Feature selection, Rating prediction using textual information, Recommender Systems}, doi = {https://doi.org/10.1016/j.ipm.2020.102304}, author = {Dionisis Margaris and Costas Vassilakis and Dimitris Spiliotopoulos} } @conference {Theodoropoulos_2019_atmf, title = {ATMF: A student-centered framework for the effective implementation of alternative teaching methods for CSEd}, booktitle = {Proceedings of the Innovative Teaching of Introductory Topics in Information Technology - 3(IT) Workshop in the context of the 19th IFIP Conference on e-Business, e-Services and e-Society (I3E 2019)}, year = {2019}, month = {01/2020}, abstract = {

The dynamic development of Informatics introduces new educational and pedagogical challenges, including the instructional design of teaching and learning. How can we teach our students better in such a growing and demanding field? Moreover, how can we motivate them and together have better learning results? This paper aims to give answers to these questions, through a student-centered framework for effectively encompassing alternative teaching methods within CS. The proposed framework (ATMF) summarizes the benefits of alternative teaching methods in contrast with known is-sues of traditional teaching. In addition, ATMF is built upon empirical evidence and concludes that alternative practices, if used under the right conditions, can provide increased motivation for learning and better learning out-comes.

}, keywords = {Alternative Teaching Methods, Computer Science Education, Teaching Framework}, doi = {10.1007/978-3-030-39634-3_11}, author = {Anastasios Theodoropoulos and Costas Vassilakis and Angela Antoniou and Manolis Wallace and Giorgos Lepouras} } @conference {Kolokotronis2019IEEESrv, title = {On Blockchain Architectures for Trust-based Collaborative Intrusion Detection}, booktitle = {Proceedings of the 1st IEEE Services Workshop on Cyber Security and Resilience in the Internet Of Things, within IEEE Services 2019}, year = {2019}, publisher = {IEEE}, organization = {IEEE}, abstract = {This paper considers the use of novel technologies for mitigating attacks that aim at compromising intrusion detection systems (IDSs). Solutions based on collaborative intrusion detection networks (CIDNs) could increase the resilience against such attacks as they allow IDS nodes to gain knowledge from each other by sharing information. However, despite the vast research in this area, trust management issues still pose significant challenges and recent works investigate whether these could be addressed by relying on blockchain and related distributed ledger technologies. Towards that direction, the paper proposes the use of a trust-based blockchain in CIDNs, referred to as trust-chain, to protect the integrity of the information shared among the CIDN peers, enhance their accountability, and secure their collaboration by thwarting insider attacks. A consensus protocol is proposed for CIDNs, which is a combination of a proof-of-stake and proof-of-work protocols, to enable collaborative IDS nodes to maintain a reliable and tampered-resistant trust-chain.}, keywords = {blockchain, collaborative intrusion detection, insider threats, security, trust management}, author = {Nicholas Kolokotronis and Sotirios Brotsis and Georgios Germanos and Costas Vassilakis and Stavros Shiaeles} } @article {vassilakis2019HV, title = {Blockchain technologies for leveraging security and privacy}, journal = {Homo Virtualis}, volume = {2}, number = {1}, year = {2019}, pages = {7{\textendash}14}, abstract = {The contemporary internet has developed into a complex ecosystem involving humans, services, applications, machines and applications that interact exchanging information, ranging from e-mail messages and social media content to crowdsourcing data and videoconferencing. In this context, a number of security threats such as viruses and malware exist, while additionally the users{\textquoteright} privacy is jeopardized by threats such as personal data leakage, usage pattern monitoring, and so forth. The IoT trend renders the Internet ecosystem even more complex, by adding a rich set of services, applications and machines, many of them backed by new user roles; these elements are weaved into everyday life and industry alike. This increases both the number of opportunities available to threat agents for exploitation and the volume and value of the underlying infrastructure and data, increasing thus the user risk level. In this paper, we explore how the Blockchain technology can be used to leverage security and privacy in the modern Internet, both by providing underpinnings for preventive measures and by facilitating digital forensic evidence collection storage, safeguarding and controlled access.}, keywords = {blockchain, Internet of Things, privacy, security}, issn = {2585-3899}, doi = {http://dx.doi.org/10.12681/homvir.20188}, url = {https://ejournals.epublishing.ekt.gr/index.php/homvir/article/view/20188}, author = {Costas Vassilakis} } @article {715, title = {Bringing a peripheral, traditional venue to the digital era with targeted narratives}, journal = {Digital Applications in Archaeology and Cultural Heritage}, volume = {14}, year = {2019}, month = {sep}, pages = {e00111}, abstract = {The current work presents a method of enhancing museum content with narratives targeting history reflection in a personalized manner, delivered by an especially designed mobile app. The mobile app is a part of a technology ecosystem that supports the visitor before, during and after her visit. Within the framework of the European H2020 CrossCult project, a method was designed, implemented and tested to enhance museum content with digital material, enriched narratives and means to actively engage visitors. In particular, the method was implemented and tested for the content of the Archaeological Museum of Tripolis (Greece) and specific content examples are presented here, together with data from visitor evaluation. The results showed that content was significantly and qualitatively enhanced and visitors recognized the potential of the app in triggering visitor curiosity, new forms of engagement, and the ability to reflect on the connections between historical and social phenomena.}, keywords = {Cultural heritage, Museum app, Narratives, reflection, Visitor experience}, doi = {10.1016/j.daach.2019.e00111}, url = {https://www.sciencedirect.com/science/article/pii/S2212054819300098}, author = {Angeliki Antoniou and Susana Reboreda Morillo and George Lepouras and Jason Diakoumakos and Costas Vassilakis and Martin Lopez Nores and Catherine Emma Jones} } @conference {717, title = {Citizen Engagement for Transparent and Accountable Policy Modelling}, booktitle = {Proceedings of the 11th International Conference on Management of Digital EcoSystems (MEDES{\textquoteright}19)}, year = {2019}, publisher = {ACM}, organization = {ACM}, abstract = {In the modern information society, learning is no longer just about obtaining factual knowledge, but more about general skills on how and where to apply available knowledge and obtain new knowledge in order to solve new problems. Such skills include abilities to connect and organize ideas, fill gaps in knowledge structures, evaluate evidence, argue with new information, test and modify, predict, clarify, generate questions, learn new concepts, make unexpected connections, reflect, analyze, synthesize and loop back. This work presents the Immersion framework, a digital ecosystem for adaptive smart learning environments for interactive mixed reality driven methods to foster learners{\textquoteright} self-regulating skill development.}, keywords = {Game-based Interaction, Learner Collaboration, Mixed Reality, Mobile Learning, Self-regulated Learning, Technology Enhanced Learning}, author = {Dimitris Spiliotopoulos and Dionisis Margaris and Costas Vassilakis} } @conference {Antoniou_2019_Mytilene, title = {Cultural technologies: the case of the Tripolis archeological museum (in Greek; Greek title: "ΠΟΛΙΤΙΣΤΙΚΕΣ ΤΕΧΝΟΛΟΓΙΕΣ: Η ΠΕΡΙΠΤΩΣΗ ΤΟΥ ΑΡΧΑΙΟΛΟΓΙΚΟΥ ΜΟΥΣΕΙΟΥ ΤΡΙΠΟΛΗΣ")}, booktitle = {Book of abstracts of the 2nd Conference of the School of Social Sciences of the University of the Aegean "Social sciences today: dilemmas and prospectives beyond the crisis"}, year = {2019}, abstract = {The Tripolis archeological museum hosts magnificent ancient art exhibits from the whole of the Arcadia county. However, a series of issues, including the old-style museological exhibition and the limited informational material offered to the visitor, combined with the lack of digital presence for the museum, lead to a low number of visitors. Culural technologies may offer solutions to these issues that the museum fronts, and to this end the museum was included in the CrossCult EU project (www.crosscult.eu). In the context of the project, the antecendents regarding the technological design for the particular museum were studied (staff, visitor and technological equipment needs), and the characteristics of the museum collections were examined. With the collaboration of the Ephorate of Antiquities of Arcadia, the most important and characteristic exhibits were identified, among those that were linked to the position of the woman in the ancient society. Using these exhibits as a basis, 7 thematic itineraries were created in both the English and the Greek language, which support the user in visiting the museum halls and exhibitions and learning certain aspects of women{\textquoteright}s lives in the antiquity (e.g. education, everyday life, social status, etc). Each exhibit is linked with different digital cultural artefacts (e.g. images from other collections, related videos, games, sound clips etc.), to create narratives that increase user engagement and stimulate reflection. In parallel, a series of games was deveped, aiming to disseminate the presence of the museum and the information sourced from it through the social networks, assist in creating user profiles and further promote the museum. Finally, user experience can continue after the visit, through the use of a specialized social network, created specifically for the needs of the museum. (Abstract in Greek follows: Το αρχαιολογικό μουσείο Τρίπολης στεγάζει καταπληκτικά δείγματα αρχαίας τέχνης από ολόκληρο τον νομό Αρκαδίας. Όμως μια σειρά προβλημάτων, όπως η παλαιού τύπου μουσειολογική έκθεση και το πολύ συνοπτικό πληροφοριακό υλικό που προσφέρεται στον επισκέπτη, μαζί με το γεγονός ότι το μουσείο δεν έχει ψηφιακή παρουσία, οδηγεί σε χαμηλή επισκεψιμότητα. Οι πολιτιστικές τεχνολογίες μπορούν να προσφέρουν λύσεις στα προβλήματα του μουσείου και έτσι το μουσείο εντάχθηκε στο Ευρωπαϊκό ερευνητικό έργο CrossCult (www.crosscult.eu). Μέσα στα πλαίσια του έργου, μελετήθηκαν τα προαπαιτούμενα σχεδιασμού τεχνολογιών για το συγκεκριμένο χώρο (ανάγκες προσωπικού, ανάγκες επισκεπτών, ανάγκες τεχνολογικού εξοπλισμού), καθώς και τα χαρακτηριστικά των συλλογών. Με τη βοήθεια της Εφορείας Αρχαιοτήτων Αρκαδίας, εντοπίστηκαν τα σημαντικότερα και χαρακτηριστικότερα εκθέματα, γύρω από το θέμα της θέσης της γυναίκας στον αρχαίο κόσμο. Με βάσει τα εκθέματα αυτά, δημιουργήθηκαν 7 θεματικές διαδρομές (σε Ελληνικά και Αγγλικά) όπου ο επισκέπτης μπορεί να περιηγηθεί στο μουσείο και να μάθει για συγκεκριμένες πτυχές της ζωής των γυναικών (π.χ. εκπαίδευση, καθημερινότητα, κοινωνική θέση, κλπ). Το κάθε έκθεμα συνδέεται με διαφορετικά ψηφιακά πολιτιστικά αντικείμενα (π.χ. εικόνες από εκθέματα άλλων συλλογών, σχετικά βίντεο, παιχνίδια, αρχεία ήχου, κλπ) για να δημιουργηθούν αφηγήσεις που να αυξάνουν τον προβληματισμό και την εμπλοκή του επισκέπτη. Παράλληλα, μια σειρά παιχνιδιών υλοποιήθηκε με σκοπό τη διάχυση στα μέσα κοινωνικής δικτύωσης για τη δημιουργία προφίλ επισκεπτών και την περαιτέρω διαφήμιση του μουσείου. Τέλος, η εμπειρία μπορεί να συνεχιστεί και μετά την επίσκεψη με τη χρήση εξειδικευμένου κοινωνικού δικτύου, φτιαγμένου ειδικά για τους επισκέπτες του μουσείου.)}, url = {https://www.propobos.gr/?id=3247\&\&atfc=3250}, author = {Angela Antoniou and Giorgos Lepouras and Costas Vassilakis and Manolis Wallace and Nikos Platis} } @conference {spiliotopoulos_2019_asonam, title = {Data-driven Country Safety Monitoring Terrorist Attack Prediction}, booktitle = {Proceedings of the 2019 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM 2019)}, year = {2019}, month = {aug}, abstract = {Terrorism is a key risk for prospective visitors of tourist desti-nations. This work reports on the analysis of past terrorist at-tack data, focusing on tourist-related attacks and attack types in Mediterranean EU area and the development of algorithms to predict terrorist attack risk levels. Data on attacks in 10 coun-tries have been analyzed to quantify the threat level of tourism-related terrorism based on the data from 2000 to 2017 and for-mulate predictions for subsequent periods. Results show that predictions on potential target types can be derived with ade-quate accuracy. Such results are useful for initiating, shifting and validating active terrorism surveillance based on real pre-dicted attack and target types per country.}, keywords = {Data Analysis, Risk Calculation, Safety Perception, Terrorist Attacks, Threat Ranking}, author = {Dimitris Spiliotopoulos and Costas Vassilakis and Dionisis Margaris} } @article {589, title = {Efficient Continuous Multi-Query Processing over Graph Streams}, journal = {CoRR}, volume = {abs/1902.05134}, year = {2019}, url = {http://arxiv.org/abs/1902.05134}, author = {Lefteris Zervakis and Vinay Setty and Christos Tryfonopoulos and Katja Hose} } @article {SODA-TR-19003, title = {Experimental results for considering Item Adoption Eagerness Information in Collaborative Filtering{\textquoteright}s Rating Prediction}, year = {2019}, month = {07/2019}, publisher = {Software and Database Systems Lab, University of the Peloponnese}, type = {Technical report}, address = {Tripolis}, abstract = {In this technical report, we present the experimental findings from applying an algorithm that considers Item Adoption Eagerness Information in the rating prediction formulation process, in order to increase rating prediction quality in Collaborative Filtering (CF). To this end, the algorithm is applied to seven datasets, which are widely used in recommender system (RS) research. The results indicate that the above algorithm introduces considerable prediction accuracy gains. }, url = {https://soda.dit.uop.gr/?q=TR-19003}, author = {Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @article {722, title = {Handling uncertainty in social media textual information for improving venue recommendation formulation quality in social networks}, journal = {Social Network Analysis and Mining}, volume = {9}, year = {2019}, month = {Oct}, pages = {64}, abstract = {One of the major problems that social media front is to continuously produce successful, user-targeted information, in the form of recommendations, which are produced by applying methods from the area of recommender systems. One of the most important applications of recommender systems in social networks is venue recommendation, targeted by the majority of the leading social networks (Facebook, TripAdvisor, OpenTable, etc.). However, recommender systems{\textquoteright} algorithms rely only on the existence of numeric ratings which are typically entered by users, and in the context of social networks, this information is scarce, since many social networks allow only reviews, rather than explicit ratings. Even if explicit ratings are supported, users may still resort to expressing their views and rating their experiences through submitting posts, which is the predominant user practice in social networks, rather than entering explicit ratings. User posts contain textual information, which can be exploited to compute derived ratings, and these derived ratings can be used in the recommendation process in the lack of explicitly entered ratings. Emerging recommender systems encompass this approach, without however tackling the fact that the ratings computed on the basis of textual information may be inaccurate, due to the very nature of the computation process. In this paper, we present an approach which extracts features of the textual information, a widely available source of information in venue category, to compute a confidence metric for the ratings that are computed from texts; then, this confidence metric is used in the user similarity computation and venue rating prediction formulation process, along with the computed rating. Furthermore, we propose a venue recommendation method that considers the generated venue rating predictions, along with venue QoS, similarity and spatial distance metrics in order to generate venue recommendations for social network users. Finally, we validate the accuracy of the rating prediction method and the user satisfaction from the recommendations generated by the recommendation formulation algorithm. Conclusively, the introduction of the confidence level significantly improves rating prediction accuracy, leverages the ability to generate personalized recommendations for users and increases user satisfaction.}, keywords = {collaborative filtering, Confidence level, Rating prediction, Recommender Systems, Social Networks, Textual information, Uncertainty, Venue recommendation formulation}, issn = {1869-5469}, doi = {10.1007/s13278-019-0610-x}, url = {https://doi.org/10.1007/s13278-019-0610-x}, author = {Dionisis Margaris and Costas Vassilakis and Spiliotopoulos, Dimitris} } @conference {margarisIISA_CIRPaC, title = {Improving Collaborative Filtering{\textquoteright}s Rating Prediction Accuracy by Introducing the Common Item Rating Past Criterion}, booktitle = {Proceedings of the 10th International Conference on Information, Intelligence, Systems and Applications (IISA2019)}, year = {2019}, month = {jul}, abstract = {Collaborative filtering computes personalized recommendations by taking into account ratings expressed by users. Collaborative filtering algorithms firstly identify people having similar tastes, by examining the likeness of already entered ratings. Users with highly similar tastes are termed {\textquotedblleft}near neighbors{\textquotedblright} and recommendations for a user are based on his near neighbors{\textquoteright} ratings. In order to measure similarity between users, so as to determine a user{\textquoteright}s NNs, a similarity metric is used. Insofar, similarity metrics proposed in the literature either consider all user ratings equally or take into account temporal variations within the users{\textquoteright} or items{\textquoteright} ratings history. However users{\textquoteright} ratings are co-shaped according to the experiences that they had in the past; therefore if two users enter similar (or dissimilar) ratings for an item while having experienced {\textendash}to a large extent the same items in the past, this constitutes stronger evidence about user similarity (or dissimilarity). Insofar however, no similarity metric takes into account this aspect. In this work, we (1) propose an algorithm that considers the common item rating past in the rating prediction computation process, aiming to improve rating prediction quality, and (2) evaluate the proposed algorithm against seven widely used datasets, both dense and sparse, and considering two widely used user similarity metrics.}, keywords = {collaborative filtering, Common Item Rating Past Criterion, Cosine Similarity, Evaluation, Items{\textquoteright} Rating Sequence, Pearson Correlation Coeffi-cient}, author = {Dionisis Margaris and Dionysios Vasilopoulos and Costas Vassilakis and Dimitris Spiliotopoulos} } @conference {margaris_iisa2019_VNNs, title = {Improving Collaborative Filtering{\textquoteright}s Rating Prediction Coverage in Sparse Datasets through the Introduction of Virtual Near Neighbors}, booktitle = {Proceedings of the 10th International Conference on Information, Intelligence, Systems and Applications (IISA2019)}, year = {2019}, month = {jul}, abstract = {Collaborative filtering creates personalized recommendations by considering ratings entered by users. Collaborative filtering algorithms initially detect users whose likings are alike, by ex-ploring the similarity between ratings that have insofar been submitted. Users having a high degree of similarity regarding their ratings are termed near neighbors, and in order to formu-late a recommendation for a user, her near neighbors{\textquoteright} ratings are extracted and form the basis for the recommendation. Col-laborative filtering algorithms however exhibit the problem commonly referred to as {\textquotedblleft}gray sheep{\textquotedblright}: this pertains to the case where for some users no near neighbors can be identified, and hence no personalized recommendations can be computed. The {\textquotedblleft}gray sheep{\textquotedblright} problem is more severe in sparse datasets, i.e. datasets where the number of ratings is small, compared to the number of items and users. In this paper, we address the {\textquotedblleft}gray sheep{\textquotedblright} problem by introducing the concept of virtual near neighbors and a related algorithm for their creation on the basis of the existing ones. We evaluate the proposed algorithm, which is termed as CFVNN, using eight widely used datasets and consid-ering two correlation metrics which are widely used in Collabo-rative Filtering research, namely the Pearson Correlation Coef-ficient and the Cosine Similarity. The results show that the pro-posed algorithm considerably leverages the capability of a Col-laborative Filtering system to compute personalized recommen-dations in the context of sparse datasets, tackling thus efficiently the {\textquotedblleft}gray sheep{\textquotedblright} problem. In parallel, the CFVNN algorithm achieves improvements in rating prediction quality, as this is expressed through the Mean Absolute Error and the Root Mean Square Error metrics.}, keywords = {collaborative filtering, Cosine Similarity, Evaluation, Pearson Correlation Coefficient, Sparse Datasets, Virtual Near Neighbors}, author = {Dionisis Margaris and Dionysios Vasilopoulos and Costas Vassilakis and Dimitris Spiliotopoulos} } @conference {716, title = {Improving Collaborative Filtering{\textquoteright}s Rating Prediction Quality by Exploiting the Item Adoption Eagerness Information}, booktitle = {Proceedings of the IEEE/WIC/ACM International Conference on Web Intelligence}, year = {2019}, publisher = {ACM}, organization = {ACM}, abstract = {Collaborative filtering computes personalized recommendations by taking into account ratings expressed by users. Collaborative filtering algorithms firstly identify people having similar tastes, who are termed as {\textquotedblleft}near neighbors" and recommendations for a user, are based on his near neighbors{\textquoteright} ratings. On the other hand, people exhibit different levels of eagerness to adopt new products: according to this characteristic, there is a set of users, termed as {\textquotedblleft}Early Adopters", who are prone to start using a product or technology as soon as it becomes available, in contrast to the majority of users, who prefer to start using items once they reach maturity; this important aspect of user behavior is not taken into account by existing algorithms. In this work, we (1) propose an algorithm that considers the eagerness shown by users to adopt products, aiming to improve rating prediction quality and (2) evaluate the proposed algorithm against seven widely used datasets.}, keywords = {collaborative filtering, Cosine Similarity, Evaluation, item adoption eagerness, Pearson Correlation Coefficient, rating prediction quality}, isbn = {978-1-4503-6934-3}, doi = {10.1145/3350546.3352544}, author = {Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @conference {725, title = {Kalamata 1821: Roads of Freedom - Digital applications teach history (Greek title: Καλαμάτα 1821: Δρόμοι Ελευθερίας {\textendash} Οι ψηφιακές εφαρμογές διδάσκουν ιστορία)}, booktitle = {2nd Panhellenic conference on Open Educational Resources and e-learning}, year = {2019}, abstract = {The {\textquotedblleft}Kalamata 1821: Roads of Freedom{\textquotedblright} project is an effort for scientifically organizing the celebration of the 200-year anniversary from the liberation of Greece from the Turkish thrall, with a special focus on the city of Kalamata. The project, aiming to link historical memories to the modern era, includes a major section related to the development of digital applications. The project{\textquoteright}s digital applications are developed by the Knowledge and Uncertainty lab of the Department of Informatics and Telecommunications of the University of the Peloponnese. The digital applications are based on the information provided by the historical scientific team of the project. Within the project, two distinct groups of applications are developed, in order to cover the diverse needs of the target population. The nature of the applications is clearly didactic, offering detailed information regarding historical facts, places and persons which relate to the Greek War of Independence, as well as on locations where important events took place. The Interactive Table applications are a group of applications which will be available to the public visiting the historic building of the old Town Hall of Kalamata, where the project exhibition center is located. These applications constitute a modern, interactive, digital encyclopedia of the relation between the city of Kalamata and the Greek War of Independence. For the Interactive Table, three original applications were developed. The first depicts histories and facts linked to some points on a map. The second presents a tree of histories, that is histories that are interrelated, and where each visitor may familiarize with facts and persons that are linked to each other. Finally, the third application focuses on images and multimedia, challenging the visitors to identify and elaborate on events and histories hiding behind pictures. The second group consists of a single application that targets on a wider public that prefers a different type on interaction. Effectively this application implements a scavenger hunt with historic content. The goal of this application is to motivate the visitor of the city of Kalamata to wander around the city, and also to link the project to the local market.}, keywords = {Educational applications, Interactive table, Mobile applications}, author = {M. Wallace and V. Poulopoulos and A. Antoniou and Costas Vassilakis and G. Lepouras and J. Diakoumakos and V. Panagiotidou} } @conference {spiliot_iisa2019, title = {A Methodology for Generated Text Annotation for High Quality Speech Synthesis}, booktitle = {Proceedings of the 10th International Conference on Information, Intelligence, Systems and Applications (IISA2019)}, year = {2019}, month = {jul}, abstract = {Natural Language Generators may produce linguistically en-riched text descriptions that can lead to significantly improved quality of speech synthesis. There are cases, however, where either the generator modules produce pieces of non-analysed, non-annotated plain text, or such modules are not available at all. Moreover, the language analysis is restricted by the usually limited domain coverage of the generator. For those cases the enriched input to the speech synthesizer needs to be produced from plain text in order to maintain speech quality. This work reports on the method for automatic domain dependent annota-tion of plain text, through the utilisation of the linguistic infor-mation from rich generated text. The synthetic speech from the resulting prosody models is evaluated by human participants showing annotation results for plain text quite on par with the rich generated text. This leads to improved perceived natural-ness of the synthesized speech.}, keywords = {Natural language generation, Natural language processing, Prosody enrichment, Semantic feature annotation, Text-to-speech}, author = {Dimitris Spiliotopoulos and Costas Vassilakis and Dionisis Margaris and Konstantinos Kotis} } @conference {718, title = {A Mixed-reality Interaction-driven Game-based Learning Framework}, booktitle = {Proceedings of the 11th International Conference on Management of Digital EcoSystems (MEDES{\textquoteright}19)}, year = {2019}, publisher = {ACM}, organization = {ACM}, abstract = {This work presents a platform for linked legislative data to engage citizens in transparent and effective democracies. With a focus on scaling up participatory approaches from local to national level, the approach extends well established and open source tools and technologies, to build mobile monitoring and analysis tools that increase transparency of law-making and implementation to citizens. This is achieved by combining open data and open services with user and citizen generated content, in order to address citizen{\textquoteright}s needs in the context of open government. Data and feeds from trusted sources are interconnected with new and re-purposed data feeds generated by users via the social web to form a meaningful, searchable, customizable, re-usable and open data-focused personalised mobile public service approach. The framework exploits the social aspects of open data, as well as the training of users, citizens and public servants to be able to understand and demand useful public open data, as well as facilitate the opening of more data.}, keywords = {Accountability, Citizen Engagement, e-government, Legislation, Mobile Public Services, Natural language processing, Policy Modelling, Transparency}, author = {Dimitris Spiliotopoulos and Dionisis Margaris and Costas Vassilakis and Volha Petukhova and Konstantinos Kotis} } @conference {714, title = {PaloAnalytics project concept, scope and outcomes: an opportunity for culture}, booktitle = {Proceedings of the Workshop on Cultural Informatics, co-located with the 14th International Workshop On Semantic And Social Media Adaptation And Personalization (SMAP 2019)}, year = {2019}, abstract = {This paper describes the national funded project entitled PaloAnalytics, which develops an innovative platform that allows companies and organizations, that operate in several countries, to monitor and analyze, in depth, the markets{\textquoteright} interest to their products and successfully plan their marketing and communication strategy, with data and insights collected from all the local media, and focuses on its application to cultural spaces and museums. In this notion, we examine the effect that this project can have in cultural spaces or companies related to arts and culture. PaloAnalytics platform allows organizations to investigate the impact of their products on consumers across different countries and this is achieved with the analysis of content from sites, blogs, social networks and open data. This implies that cultural organization can benefit by adopting the implemented services, so that the can recognize and analyze their audience, their online marketing campaigns as well as examine the impact of their messages and the spread of their messages on the Internet. In this paper, we briefly describe the project and discuss on the impact on cultural related organizations.}, keywords = {big data, data monitoring, Data visualization, deep learning, influencers, infographics, trending topics}, url = {http://ceur-ws.org/Vol-2412/paper7.pdf}, author = {Vassilis Poulopoulos and Manolis Wallace and Costas Vassilakis and George Lepouras}, editor = {Angeliki Antoniou and Manolis Wallace} } @conference {DBLP:conf/debs/ChantziosZST19, title = {Ping - A customizable, open-source information filtering system for textual data}, booktitle = {Proceedings of the 13th ACM International Conference on Distributed and Event-based Systems, DEBS 2019, Darmstadt, Germany, June 24-28, 2019.}, year = {2019}, pages = {228{\textendash}231}, doi = {10.1145/3328905.3332512}, url = {https://doi.org/10.1145/3328905.3332512}, author = {Thanasis Chantzios and Lefteris Zervakis and Spiros Skiadopoulos and Christos Tryfonopoulos} } @proceedings {DBLP:conf/debs/2019, title = {Proceedings of the 13th ACM International Conference on Distributed and Event-based Systems, DEBS 2019, Darmstadt, Germany, June 24-28, 2019}, year = {2019}, publisher = {ACM}, isbn = {978-1-4503-6794-3}, url = {https://dl.acm.org/citation.cfm?id=3328905} } @conference {588, title = {The quest for the appropriate cyber-threat intelligence sharing platform}, booktitle = {Proceedings of the 8th International Conference on Data Science, Technology and Applications (DATA), Prague, Czech Republic}, year = {2019}, month = { 07/2009}, abstract = {Cyber-threat intelligence (CTI) is any information that can help an organization identify, assess, monitor, and respond to cyber-threats. It relates to all cyber components of an organization such as networks, computers, and other types of information technology. In the recent years, due to the major increase of cyber-threats, CTI sharing is becoming increasingly important both as a subject of research and as a concept of providing additional security to organizations. However, selecting the proper tools and platforms for CTI sharing, is a challenging task, that pertains to a variety of aspects. In this paper, we start by overviewing the CTI procedure (threat types, categories, sources and the general CTI life-cycle). Then, we present a set of seven high-level CTI platform recommendations that can be used to evaluate a platform and subsequently we survey six state-of- the-art cyber-threat intelligence platforms. Finally, we compare and evaluate the six aforementioned platforms by means of the earlier proposed recommendations.}, keywords = {Cyber-threat, Intelligence, Sharing}, url = {http://users.uop.gr/~trifon/papers/pdf/data19-CKSKTBK.pdf}, author = {Thanasis Chantzios and Paris Koloveas and Spiros Skiadopoulos and Nikos Kolokotronis and Christos Tryfonopoulos and Vasiliki-Georgia Bilali and Dimitris Kavallieros} } @conference {726, title = {Scavenger Hunt in the Roads of Freedom (Greek title: {\textquotedblleft}Κυνήγι θησαυρού στους Δρόμους της Ελευθερίας")}, booktitle = {Proceedings of the 3nd Pan-Hellenic Conference on Digital Cultural Heritage-EuroMed 2019}, year = {2019}, abstract = {The project "Kalamata 1821: Roads of freedom" is being funded in the context of the Action "RESEARCH - CREATE - INNOVATE. The project, which encompasses original historic research work in the University of the Peloponnese, is an effort to narrate a historic course of 200 years for the city of Kalamata, from the eruption of the Greek revolution until today, through a modern and fresh perspective. This paper will present one of the digital applications developed within the project, and more specifically the Scavenger Hunt that is being developed by the Knowledge and Uncertainty lab of the Department of Informatics and Telecommunications in Tripolis. The game is designed for mobile devices and its goal is to link the historic content of the project with the contemporary city and, in a gamified fashion, assist the user not only to familiarize with the history of the city but also to navigate in the city and connect with the local market. By searching through pictures of various locations of the city, the visitor is directed to the most outstanding locations of the war of independence, and learns about the contribution of the city of Kalamata in this turning point for the history of the Greek nation. At the same time, the visitor is rewarded by receiving offers for local stores.}, keywords = {Greek War of Independence, Kalamata, Roads of Freedom, Scavenger Hunt}, author = {Manolis Wallace and Vassilis Poulopoulos and George Lepouras and Costas Vassilakis and Angeliki Antoniou} } @proceedings {590, title = {SciTo trends: visualising scientific topic trends}, year = {2019}, month = {September}, author = {Serafeim Chatzopoulos and Panagiotis Deligiannis and Thanasis Vergoulis and Ilias Kanellos and Christos Tryfonopoulos and Theodore Dalamagas} } @conference {Margaris_2019_asonam, title = {Social Relations versus Near Neighbours: Reliable Recommenders in Limited Information Social Network Collaborative Filtering for Online Advertising}, booktitle = {Proceedings of the 2019 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM 2019)}, year = {2019}, month = {aug}, abstract = {Online advertising benefits by recommender systems since the latter analyse reviews and rating of products, providing useful insight of the buyer perception of products and services. When traditional recommender system information is enriched with social network information, more successful recommendations are produced, since more users{\textquoteright} aspects are taken into consid-eration. However, social network information may be unavaila-ble since some users may not have social network accounts or may not consent to their use for recommendations, while rating data may be unavailable due to the cold start phenomenon. In this paper, we propose an algorithm that combines limited col-laborative filtering information, comprised only of users{\textquoteright} ratings on items, with limited social network information, com-prised only of users{\textquoteright} social relations, in order to improve (1) prediction accuracy and (2) prediction coverage in collaborative filtering recommender systems, at the same time. The proposed algorithm considerably improves rating prediction accuracy and coverage, while it can be easily integrated in recommender systems.}, keywords = {collaborative filtering, Evaluation, Limited Information, Near Neighbours, Online Advertising, Pearson Correlation Coefficient, Social Networks}, author = {Dionisis Margaris and Dimitris Spiliotopoulos and Costas Vassilakis} } @conference {727, title = {Supporting small museums through social network semantic analysis (Greek title: Υποστήριξη μικρών μουσείων μέσω της σημασιολογικής ανάλυσης κοινωνικών δικτύων)}, booktitle = {Proceedings of the 3nd Pan-Hellenic Conference on Digital Cultural Heritage-EuroMed 2019}, year = {2019}, abstract = {Greece has a significant historic, archaeological and cultural wealth, and a big number of museums and related venues. Some of them are big, both in size and resources -human as well as financial. Most venues however are small in size, are not connected with larger organizations, have constrained budgets and little or no permanent staff. In this paper, we focus on that particular category of museums. Many of these museums possess noteworthy collections, and it would be desirable if the general public could enjoy them. Unfortunately, in most cases, even the existence of the museums is not generally known, even to inhabitants of the cities at which the museums are located. The small number of visitors leads to confined revenues, and this in turn leads to a situation which is not financially viable. In order for a small museum to survive, its existence and value must be made known to the wide public. However, this is inhibited due to the lack of resources to finance advertising and the lack of specialized personnel. In this paper, we combine our experiences on small museums, which has been developed within the CrossCult H2020 project, with know-how on social network analysis which has been gained in the context of the PaloAnalytics national project, in order to offer viable solutions for promotion, which are tailored to the needs of small museums.}, keywords = {semantic analysis, small-sized museums, Social Networks}, author = {Manolis Wallace and Vassilis Poulopoulos and George Lepouras and Costas Vassilakis and Angeliki Antoniou} } @conference {724, title = {TripMentor: Challenges and prospects for culture and tourism in the Attica region (Greek title: {\textquotedblleft}TripMentor: προκλήσεις και προοπτικές για τον πολιτισμό και τον τουρισμό στην περιφέρεια Αττικής{\textquotedblleft})}, booktitle = {Proceedings of the 3nd Pan-Hellenic Conference on Digital Cultural Heritage-EuroMed 2019}, year = {2019}, abstract = {This paper presents the TripMentor project which is related to the tourism and civilization in the region of Attica. The main goal of the project is the presentation, in two languages, of the rich cultural content of the region to the tourists, through an Internet-based environment and through mobile applications. The goal of the project is to guide the visitors through many possible alternative routes, which include points of interest, as well as enterprises with tourism-related offers, while at the same time attempts to combine these routes with cultural points of interest. The project interrelates information, venues and visitor profiles with an automated way, striving to offer a unique personalized experience, tailored to the needs and preferences of each user. The project challenges are mainly technical, since through the project procedures (a) information regarding the points of interest should be gathered in an automated fashion (b) information about events related to points of interest must be taken into account and (v) data related to users, and especially the user profiles must be discovered and exploited so that the available information can be synthesized into a unique experience. In this context, we present the project application domain and the related challenges.}, keywords = {cultural information, culture, geospatial data, Social Networks, tourism, visitor profile}, author = {Costas Vassilakis and Vassilis Poulopoulos and Manolis Wallace and Angeliki Antoniou and George Lepouras} } @conference {713, title = {TripMentor Project: scope and challenges}, booktitle = {Proceedings of the Workshop on Cultural Informatics, co-located with the 14th International Workshop On Semantic And Social Media Adaptation And Personalization (SMAP 2019)}, year = {2019}, abstract = {We present Tripmentor, a novel project, that is related to tourism in the region of Attica. The project has as main scope to provide rich media content to tourists through a web and mobile environment in two languages trying to guide them through alternative routes that include places of interest as well as organizations with offers to tourists. The project interconnects people with places and events in an automated manner trying to personalize on each tourist{\textquoteright}s personality. The challenges of the project are mainly technological as through the processes of the project a) automated information about venues must be collected, b) information about events related to venues must be fetched and finally c) data related to system users and mainly their profile should be discovered and created in order to offer a unique experience to each of them. We present the scope of the project as well as the challenges of its implementation.}, keywords = {cultural related information, geodata, personalization, social media, tourism, tripmentor}, url = {http://ceur-ws.org/Vol-2412/paper6.pdf}, author = {Costas Vassilakis and Vassilis Poulopoulos and Manolis Wallace and Angeliki Antoniou and George Lepouras}, editor = {Angeliki Antoniou and Manolis Wallace} } @article {DBLP:journals/bdr/Chatzigeorgakidis19, title = {Visual Exploration of Geolocated Time Series with Hybrid Indexing}, journal = {Big Data Research}, volume = {15}, year = {2019}, pages = {12{\textendash}28}, doi = {10.1016/j.bdr.2019.02.001}, url = {https://doi.org/10.1016/j.bdr.2019.02.001}, author = {Georgios Chatzigeorgakidis and Kostas Patroumpas and Dimitrios Skoutas and Spiros Athanasiou and Spiros Skiadopoulos} } @proceedings {DBLP:conf/pakdd/2018-2, title = {Advances in Knowledge Discovery and Data Mining - 22nd Pacific-Asia Conference, PAKDD 2018, Melbourne, VIC, Australia, June 3-6, 2018, Proceedings, Part II}, volume = {10938}, year = {2018}, publisher = {Springer}, isbn = {978-3-319-93036-7}, doi = {10.1007/978-3-319-93037-4}, url = {https://doi.org/10.1007/978-3-319-93037-4}, editor = {Dinh Q. Phung and Vincent S. Tseng and Geoffrey I. Webb and Bao Ho and Mohadeseh Ganji and Lida Rashidi} } @inbook {Vasilakis2018BigData, title = {Big Data Platforms and Applications}, year = {2018}, publisher = {Springer}, organization = {Springer}, chapter = {exhiSTORY: Smart self-organizing exhibits}, abstract = {Creating stories for exhibitions is a fascinating and in parallel laborious task. As every exhibition is designed to tell a story, museum curators are responsible for identifying, for each exhibit, its aspects that fit to the message of the story and position the exhibit at the right place in the story thread. In this context we analyze how the technological advances in the fields of sensors and Internet of Things can be utilized in order to construct a "smart space", which consists of self-organizing exhibits that cooperate with each other and provide visitors with comprehensible, rich, diverse, personalized and highly stimulating experiences. We present the system named "exhiSTORY" that intends to provide the appropriate infrastructure to be used in museums and places where exhibitions are held in order to support smart exhibits. The architecture of the system and its application potential is presented and discussed.}, author = {Costas Vassilakis and Vassilis Poulopoulos and Angela Antoniou and Manolis Wallace and Giorgos Lepouras and Martin Lopez Nores}, editor = {TBC} } @inbook {DBLP:reference/db/Skiadopoulos18, title = {Cardinal Direction Relationships}, booktitle = {Encyclopedia of Database Systems, Second Edition}, year = {2018}, doi = {10.1007/978-1-4614-8265-9_45}, url = {https://doi.org/10.1007/978-1-4614-8265-9_45}, author = {Spiros Skiadopoulos} } @conference {545, title = {Data Science Tutor: An online platform for automated exercise solving in Data Science}, booktitle = {Proceedings of the 9th Conference on Computer Science Teaching (DIDINFO)}, year = {2018}, month = {October}, address = {Thessaloniki, Greece}, author = {Christos Tryfonopoulos and Charis Kotsiopoulos and Paraskevi Raftopoulou} } @conference {561, title = {The Effect of Introducing Content Price in Distributed Social Networks}, booktitle = {Proceedings of the 23rd Conference on Information Technologies (IT)}, year = {2018}, month = {March}, address = {Kaunas, Lithuania}, author = {Christos Tryfonopoulos} } @conference {poulopoulos2018a, title = {The Effect of Social Media Trending Topics Related to Cultural Venues{\textquoteright} Content}, booktitle = {2018 13th International Workshop on Semantic and Social Media Adaptation and Personalization (SMAP)}, year = {2018}, month = {sep}, publisher = {IEEE}, organization = {IEEE}, abstract = {Social media have gained the majority of attention on the Internet having an extreme number of daily visitors worldwide. The amount of information exchanged is vast, while users have become equally producers and consumers of data. Words like {\textquotedblleft}trending{\textquotedblright}, {\textquotedblleft}influencers{\textquotedblright}, {\textquotedblleft}likes{\textquotedblright} and {\textquotedblleft}viral{\textquotedblright} are in the daily agenda of data analyzers, as they are associated with factors that play an important role in the influence of social media content to its audience. These aspects are nowadays strongly taken into account by organizations that want to draw the public{\textquoteright}s attention to the content they deliver, and in this context cultural institutions have already started to take under great consideration not only their presence in social media, but also the exploitation of social media dynamics. In this paper we propose a method that can enable cultural venues to benefit from matches between their own content and ongoing discussions on social media. More specifically we extract trending topics that can be related semantically with the content of a cultural institute and examine how a venue can benefit by exploiting these matches. The proposed algorithm has been developed in the scope of the {\textquotedblleft}CrossCult{\textquotedblright} H2020 project, and has been experimentally tested by analyzing the case of Twitter in Greek language.}, keywords = {cultural informatics, cultural venues, personalization, social media, trending topics}, doi = {10.1109/SMAP.2018.8501878}, author = {Vassilis Poulopoulos and Costas Vassilakis and Manolis Wallace and Angela Antoniou and Giorgos Lepouras} } @conference {578, title = {Efficient and Expressive Semantic Information Push for Cultural Heritage Applications}, booktitle = {Proceedings of the International Workshop on Semantic Web for Cultural Heritage (SW4CH @ ESWC)}, year = {2018}, month = {March}, address = {Crete, Greece}, author = {Christos Tryfonopoulos} } @book {DBLP:reference/db/2018, title = {Encyclopedia of Database Systems, Second Edition}, year = {2018}, publisher = {Springer}, organization = {Springer}, isbn = {978-1-4614-8266-6}, doi = {10.1007/978-1-4614-8265-9}, url = {https://doi.org/10.1007/978-1-4614-8265-9}, editor = {Ling Liu and M. Tamer {\"O}zsu} } @article {margaris2018tldks, title = {Enhancing Rating Prediction Quality Through Improving the Accuracy of Detection of Shifts in Rating Practices}, journal = {Lecture Notes in Computer Science}, volume = {10940 (LNCS)}, number = {XXXVII}, year = {2018}, pages = {151{\textendash}191}, publisher = {Springer Berlin Heidelberg}, abstract = {The most widely used similarity metrics in collaborative filtering, namely the Pearson Correlation and the Adjusted Cosine Similarity, adjust each individual rating by the mean of the ratings entered by the specific user, when computing similarities, due to the fact that users follow different rating practices, in the sense that some are stricter when rating items, while others are more lenient. However, a user{\textquoteright}s rating practices change over time, i.e. a user could start as lenient and subsequently become stricter or vice versa; hence by relying on a single mean value per user, we fail to follow such shifts in users{\textquoteright} rating practices, leading to decreased rating prediction accuracy. In this work, we present a novel algorithm for calculating dynamic user averages, i.e. time-in-point averages that follow shifts in users{\textquoteright} rating practices, and exploit them in both user-user and item-item collaborative filtering implementations. The proposed algorithm has been found to introduce significant gains in rating prediction accuracy, and outperforms other dynamic average computation approaches that are presented in the literature.}, doi = {10.1007/978-3-662-57932-9_5}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {mathas2018a, title = {Evaluation of Apache Spot\textquotesingles machine learning capabilities in an SDN/NFV enabled environment}, booktitle = {Proceedings of the 13th International Conference on Availability, Reliability and Security - ARES 2018}, year = {2018}, publisher = {ACM Press}, organization = {ACM Press}, abstract = {Software Defined Networking (SDN) and Network Function Virtualisation (NFV) are transforming modern networks towards a service-oriented architecture. At the same time, the cybersecurity industry is rapidly adopting Machine Learning (ML) algorithms to improve detection and mitigation of complex attacks. Traditional intrusion detection systems perform signature-based detection, based on well-known malicious traffic patterns that signify potential attacks. The main drawback of this method is that attack patterns need to be known in advance and signatures must be preconfigured. Hence, typical systems fail to detect a zero-day attack or an attack with unknown signature. This work considers the use of machine learning for advanced anomaly detection, and specifically deploys the Apache Spot ML framework on an SDN/NFV-enabled testbed running cybersecurity services as Virtual Network Functions (VNFs). VNFs are used to capture traffic for ingestion by the ML algorithm and apply mitigation measures in case of a detected anomaly. Apache Spot utilises Latent Dirichlet Allocation to identify anomalous traffic patterns in Netflow, DNS and proxy data. We evaluate the overall performance of Apache Spot by deploying Denial of Service (Slowloris, BoNeSi) and a Data Exfiltration attack (iodine).}, keywords = {Apache Spot, Latent Dirichlet Allocation, Machine Learning, Network Function Virtualisation, Penetration Testing, SHIELD Project�, Software Defined Networking}, doi = {10.1145/3230833.3233278}, author = {Christos M. Mathas and Olga E. Segou and Georgios Xylouris and Dimitris Christinakis and Michail-Alexandros Kourtis and Costas Vassilakis and Anastasios Kourtis} } @conference {PoulopoulosGIIS2018, title = {ExhiSTORY: IoT in the service of Cultural Heritage}, booktitle = {Proceedings of the Global Information Infrastructure and Networking Symposium (GIIS 2018), Special Session on IoT and Cultural Heritage Protection}, year = {2018}, month = {oct}, publisher = {IEEE}, organization = {IEEE}, abstract = {Creating stories for exhibitions is a fascinating and in parallel laborious task. As every exhibition is designed to tell a story, museum curators are responsible for analyzing each exhibit in order to extract messages that form a story and position accordingly the objects in correct order within the museum space. In this context, we analyze how the technological advances in the fields of sensors and the Internet of Things can be utilized in order to construct a {\textquotedblleft}smart space{\textquotedblright}, where exhibits can communicate with the visitors and to each other and can be organized automatically so that they can generate rich, personalized, coherent and highly stimulating experiences. We present the architecture of the system named {\textquotedblleft}exhiSTORY{\textquotedblright}, that intends to provide the appropriate infrastructure to be used in museums and places where exhibitions are held, in order to support smart exhibits. We discuss and analyze the architecture of the system and the ways of its application in a cultural space.}, doi = {10.1109/GIIS.2018.8635759}, author = {Vassilis Poulopoulos and Costas Vassilakis and Angela Antoniou and Manolis Wallace and Giorgos Lepouras and Martin Lopez Nores} } @article {Vassilakis_fgcs17, title = {exhiSTORY: Smart Exhibits That Tell Their Own Stories}, journal = {Future Generation of Computer Systems}, volume = {81}, year = {2018}, pages = {542-556}, abstract = {Museum exhibitions are designed to tell a story; this story is woven by curators and in its context a particular aspect of each exhibit, fitting to the message that the story is intended to convey, is highlighted. Adding new exhibits to the story requires curators to identify for each exhibit its aspects that fit to the message of the story and position the exhibit at the right place in the story thread. The availability of rich semantic information for exhibits, allows for exploiting the wealth of meanings that museum exhibits express, enabling the automated or semi-automated generation of practically countless stories that can be told. Personalization algorithms can then be employed to choose from these stories the ones most suitable for each individual user, based on the semantics of the stories and information within the user profile. In this work we examine how opportunities arising from technological advances in the fields of IoT and semantics can be used to develop smart, self-organizing exhibits that cooperate with each other and provide visitors with comprehensible, rich, diverse, personalized and highly stimulating experiences. These notions are included in the design of a system named exhiSTORY, which also exploits previously ignored information and identifies previously unseen semantic links. We present the architecture of the system and discuss its application potential.}, keywords = {Cultural heritage, IoT, personalization, Quality of Experience (QoE), Self-organizing exhibitions, semantics}, doi = {https://doi.org/10.1016/j.future.2017.10.038}, url = {https://www.sciencedirect.com/science/article/pii/S0167739X17324093}, author = {Costas Vassilakis and Vassilis Poulopoulos and Angela Antoniou and Manolis Wallace and Giorgos Lepouras and Martin Lopez Nores} } @article {margaris2018a, title = {Exploiting Rating Abstention Intervals for Addressing Concept Drift in Social Network Recommender Systems}, journal = {Informatics}, volume = {5}, number = {2}, year = {2018}, month = {apr}, pages = {21 pages}, abstract = {One of the major problems that social networks face is the continuous production of successful, user-targeted information in the form of recommendations, which are produced exploiting technology from the field of recommender systems. Recommender systems are based on information about users{\textquoteright} past behavior to formulate recommendations about their future actions. However, as time goes by, social network users may change preferences and likings: they may like different types of clothes, listen to different singers or even different genres of music and so on. This phenomenon has been termed as concept drift. In this paper: (1) we establish that when a social network user abstains from rating submission for a long time, it is a strong indication that concept drift has occurred and (2) we present a technique that exploits the abstention interval concept, to drop from the database ratings that do not reflect the current social network user{\textquoteright}s interests, thus improving prediction quality.}, keywords = {collaborative filtering, concept drift, Evaluation, Recommender Systems, shift of interest, Social Networks}, doi = {10.3390/informatics5020021}, url = {http://www.mdpi.com/2227-9709/5/2/21}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {DBLP:conf/ssdbm/KaffesBSS18, title = {Finding shortest keyword covering routes in road networks}, booktitle = {Proceedings of the 30th International Conference on Scientific and Statistical Database Management, SSDBM 2018, Bozen-Bolzano, Italy, July 09-11, 2018}, year = {2018}, pages = {12:1{\textendash}12:12}, doi = {10.1145/3221269.3223038}, url = {https://doi.org/10.1145/3221269.3223038}, author = {Vassilis Kaffes and Alexandros Belesiotis and Dimitrios Skoutas and Spiros Skiadopoulos} } @article {DBLP:journals/jbd/Chatzigeorgakidis18, title = {FML-kNN: scalable machine learning on Big Data using \emphk-nearest neighbor joins}, journal = {J. Big Data}, volume = {5}, year = {2018}, pages = {4}, doi = {10.1186/s40537-018-0115-x}, url = {https://doi.org/10.1186/s40537-018-0115-x}, author = {Georgios Chatzigeorgakidis and Sophia Karagiorgou and Spiros Athanasiou and Spiros Skiadopoulos} } @conference {angelantEuromed18, title = {The Human Computer Interaction and Virtual Reality Lab (University of Peloponnese): overview and current challenges}, booktitle = {Proceedings of the {\textquotedblleft}Cultural informatics research and applications: State of the art and open challenges{\textquotedblright} workshop, within the Euromed 2018 Conference}, year = {2018}, month = {oct}, abstract = {The Human-Computer Interaction and Virtual Reality Lab, at the Department of Informatics and Telecommunications of the University of Peloponnese, aims to conduct high quality research in areas related to the analysis, design, develop-ment, and evaluation of HCI and VR systems and applications, and in parallel to support the teaching requirements of the department in the respective field. Over the last years the HCI-VR lab particularly focuses on Cultural Heritage and de-velops technologies primarily for spaces of cultural heritage that cover the diverse needs of heterogeneous audiences providing holistic visitor experience. The HCI-VR lab is actively participating in National and European projects on Cultural Heritage, such as FP7 Experimedia (https://hci-vr.dit.uop.gr/experimedia), H2020 CrossCult (www.crosscult.eu) and multiple projects from the National Strategic Reference Framework.}, url = {http://ceur-ws.org/Vol-2235/paper10.pdf}, author = {Angela Antoniou and Costas Vassilakis and Anastasios Theodoropoulos and Giorgos Lepouras} } @article {DBLP:journals/dke/AllamSK18, title = {Improved suffix blocking for record linkage and entity resolution}, journal = {Data Knowl. Eng.}, volume = {117}, year = {2018}, pages = {98{\textendash}113}, doi = {10.1016/j.datak.2018.07.005}, url = {https://doi.org/10.1016/j.datak.2018.07.005}, author = {Amin Allam and Spiros Skiadopoulos and Panos Kalnis} } @conference {margarisDatacom2018a, title = {Improving Collaborative Filtering{\textquoteright}s Rating Prediction Accuracy by Considering Users{\textquoteright} Rating Variability}, booktitle = {2018 IEEE 16th Intl Conf on Dependable, Autonomic and Secure Computing, 16th Intl Conf on Pervasive Intelligence and Computing, 4th Intl Conf on Big Data Intelligence and Computing and Cyber Science and Technology Congress(DASC/PiCom/DataCom/CyberSciTech)}, year = {2018}, publisher = {IEEE}, organization = {IEEE}, abstract = {When rating predictions are computed in user-user collaborative filtering, each individual rating is typically adjusted by the mean of the ratings entered by the specific user. This practice takes into account the fact that users follow different rating practices, in the sense that some are stricter when rating items, while others are more lenient. However, users{\textquoteright} rating practices may also differ in rating variability, in the sense that some user may be entering ratings close to her mean, while another user may be entering more extreme ratings, close to the limits of the rating scale. In this work, we (1) propose an algorithm that considers users{\textquoteright} ratings variability in the rating prediction computation process, aiming to improve rating prediction quality and (2) evaluate the proposed algorithm against seven widely used datasets considering three widely used variability measures and two user similarity metrics. The proposed algorithm, using the {\textquotedblleft}mean absolute deviation around the mean{\textquotedblright} variability measure, has been found to intro-duce considerable gains in rating prediction accuracy, in every dataset and under both user similarity metrics tested.}, keywords = {collaborative filtering, Cosine Similarity, Evaluation, Pearson Correlation Coefficient, Users{\textquoteright} Ratings Variability}, doi = {10.1109/DASC/PiCom/DataCom/CyberSciTec.2018.00145}, url = {https://ieeexplore.ieee.org/document/8512012}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {margarisDatacom2018b, title = {Improving Collaborative Filtering{\textquoteright}s Rating Prediction Coverage in Sparse Datasets by Exploiting User Dissimilarity}, booktitle = {2018 IEEE 16th Intl Conf on Dependable, Autonomic and Secure Computing, 16th Intl Conf on Pervasive Intelligence and Computing, 4th Intl Conf on Big Data Intelligence and Computing and Cyber Science and Technology Congress(DASC/PiCom/DataCom/CyberSciTech)}, year = {2018}, month = {aug}, publisher = {IEEE}, organization = {IEEE}, abstract = {Collaborative filtering systems analyze the ratings databases to identify users with similar likings and preferences, termed as near neighbors, and then generate rating predictions for a user by examining the ratings of his near neighbors for items that the user has not yet rated; based on rating predictions, recommenda-tions are then formulated. However, these systems are known to exhibit the {\textquotedblleft}gray sheep{\textquotedblright} problem, i.e. the situation where no near neighbors can be identified for a number of users, and hence no recommendation can be formulated for them. This problem is more intense in sparse datasets, i.e. datasets with relatively small number of ratings, compared to the number of users and items. In this work, we propose a method for alleviating this problem by exploiting user dissimilarity, under the assumption that if some users have exhibited opposing preferences in the past, they are likely to do so in the future. The proposed method has been eval-uated against seven widely used datasets and has been proven to be particularly effective in increasing the percentage of users for which personalized recommendations can be formulated in the context of sparse datasets, while at the same time maintaining or slightly improving rating prediction quality.}, keywords = {collaborative filtering, Evaluation, Negative Correlation, Pearson Correlation Coefficient, Sparse Datasets, User-User Correlation}, doi = {10.1109/dasc/picom/datacom/cyberscitec.2018.00150}, url = {https://ieeexplore.ieee.org/document/8512017}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {DBLP:conf/edbt/Chatzigeorgakidis18, title = {Map-Based Visual Exploration of Geolocated Time Series}, booktitle = {Proceedings of the Workshops of the EDBT/ICDT 2018 Joint Conference (EDBT/ICDT 2018), Vienna, Austria, March 26, 2018.}, year = {2018}, pages = {92{\textendash}99}, url = {http://ceur-ws.org/Vol-2083/paper-14.pdf}, author = {Georgios Chatzigeorgakidis and Dimitrios Skoutas and Kostas Patroumpas and Spiros Athanasiou and Spiros Skiadopoulos} } @conference {558, title = {A Methodology for the Automatic Creation of Massive Continuous Query Datasets from Real-Life Corpora}, booktitle = {Proceedings of the 7th International Conference on Advanced Computer Science and Information Technology (ICAIT)}, year = {2018}, month = {April}, address = {Vienna, Austria}, author = {Christos Tryfonopoulos} } @article {DBLP:journals/tpds/JamourSK18, title = {Parallel Algorithm for Incremental Betweenness Centrality on Large Graphs}, journal = {IEEE Trans. Parallel Distrib. Syst.}, volume = {29}, number = {3}, year = {2018}, pages = {659{\textendash}672}, doi = {10.1109/TPDS.2017.2763951}, url = {https://doi.org/10.1109/TPDS.2017.2763951}, author = {Fuad Jamour and Spiros Skiadopoulos and Panos Kalnis} } @conference {vacilosEuromed18, title = {Personality Analysis of Social Media Influencers as a Tool for Cultural Institutions}, booktitle = {Digital Heritage. Progress in Cultural Heritage: Documentation, Preservation, and Protection}, year = {2018}, pages = {236{\textendash}247}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {Nowadays, more and more cultural venues tend to utilize social media as a main tool for marketing, spreading their messages, engaging public and raising public awareness towards culture. It comes to a point where the massive of content in social media makes it a tedious procedure to contact the appropriate audience, the people that would really be stimulated by cultural information. In this notion, we assume that establishing conversations of high impact can possibly guide the cultural venues to audiences that can benefit more. These conversations usually include the so called influencers, users whose opinion can affect many people on social media; the latter usually referred to as followers. In this research paper we examine the characteristics of the influencers that can affect the procedures of a cultural venue on social media. The research is done within the scope of "CrossCult" EU funded project.}, keywords = {cultural informatics, influencers, personality traits, social media, user modeling}, doi = {10.1007/978-3-030-01762-0_20}, author = {Vassilis Poulopoulos and Costas Vassilakis and Angela Antoniou and Giorgos Lepouras and Manolis Wallace} } @article {Poulopoulos2018Heritage, title = {The personality of the influencers, the characteristics of qualitative discussions and their analysis for recommendations to cultural institutions}, journal = {Heritage}, volume = {1}, number = {2}, year = {2018}, month = {oct}, pages = {239-253}, abstract = {Social media usage is affecting peoples{\textquoteright} views through opinion sharing, a fact that has started to attract cultural institutions, as it is possible that this procedure can possibly be a part of a museum experience. As the main goal of a cultural institution is the maximization of senses stimulation, the device that is offered to the visitors{\textquoteright} hands everyday and every moment, becomes an important tool for the art spaces. In this notion we perform research on issues that can be of great importance for the museum{\textquoteright}s online presence and attraction. We focus on establishing the personality of influencers related to culture, as well as the characteristics of qualitative discussions on the social media. Crosscult Project is an EU funded project, that aims to spur a change in the way European citizens appraise History, and sets that basis of our research as the experiments are conducted within its scope of. Through the experimental procedure, we collect information in order to define the character of the influencer and the substances of a {\textquotedblleft}serious{\textquotedblright} conversation. {\textquotedblleft}Serious{\textquotedblright} conversations are regarded the ones in which a cultural organization can participate actively and benefit from the participation. We present the results of our experimental evaluation and analyze how cultural institutions can benefit from the outcomes of our research.}, keywords = {cultural informatics, digital humanities, personality traits, personalization, serious conversations, social media influencers, user modeling}, issn = {2571-9408}, doi = {10.3390/heritage1020016}, url = {https://doi.org/10.3390/heritage1020016}, author = {Vassilis Poulopoulos and Costas Vassilakis and Angela Antoniou and Giorgos Lepouras and Anastasios Theodoropoulos and Manolis Wallace} } @proceedings {DBLP:conf/gis/2018, title = {Proceedings of the 26th ACM SIGSPATIAL International Conference on Advances in Geographic Information Systems, SIGSPATIAL 2018, Seattle, WA, USA, November 06-09, 2018}, year = {2018}, publisher = {ACM}, isbn = {978-1-4503-5889-7}, url = {http://dl.acm.org/citation.cfm?id=3274895}, editor = {Farnoush Banaei Kashani and Erik G. Hoel and Ralf Hartmut G{\"u}ting and Roberto Tamassia and Li Xiong} } @proceedings {DBLP:conf/ssdbm/2018, title = {Proceedings of the 30th International Conference on Scientific and Statistical Database Management, SSDBM 2018, Bozen-Bolzano, Italy, July 09-11, 2018}, year = {2018}, publisher = {ACM}, doi = {10.1145/3221269}, url = {https://doi.org/10.1145/3221269}, editor = {Dimitris Sacharidis and Johann Gamper and Michael H. B{\"o}hlen} } @proceedings {DBLP:conf/edbt/2018w, title = {Proceedings of the Workshops of the EDBT/ICDT 2018 Joint Conference (EDBT/ICDT 2018), Vienna, Austria, March 26, 2018}, volume = {2083}, year = {2018}, publisher = {CEUR-WS.org}, url = {http://ceur-ws.org/Vol-2083}, editor = {Nikolaus Augsten} } @conference {DBLP:conf/gis/Chatzigeorgakidis18, title = {Scalable hybrid similarity join over geolocated time series}, booktitle = {Proceedings of the 26th ACM SIGSPATIAL International Conference on Advances in Geographic Information Systems, SIGSPATIAL 2018, Seattle, WA, USA, November 06-09, 2018}, year = {2018}, pages = {119{\textendash}128}, doi = {10.1145/3274895.3274949}, url = {https://doi.org/10.1145/3274895.3274949}, author = {Georgios Chatzigeorgakidis and Kostas Patroumpas and Dimitrios Skoutas and Spiros Athanasiou and Spiros Skiadopoulos} } @conference {DBLP:conf/pakdd/ChronisGAS18, title = {Unsupervised Disaggregation of Low Granularity Resource Consumption Time Series}, booktitle = {Advances in Knowledge Discovery and Data Mining - 22nd Pacific-Asia Conference, PAKDD 2018, Melbourne, VIC, Australia, June 3-6, 2018, Proceedings, Part II}, year = {2018}, pages = {558{\textendash}570}, doi = {10.1007/978-3-319-93037-4_44}, url = {https://doi.org/10.1007/978-3-319-93037-4_44}, author = {Pantelis Chronis and Giorgos Giannopoulos and Spiros Athanasiou and Spiros Skiadopoulos} } @article {DBLP:journals/jbi/PoulisLSG17, title = {Anonymizing datasets with demographics and diagnosis codes in the presence of utility constraints}, journal = {Journal of Biomedical Informatics}, volume = {65}, year = {2017}, pages = {76{\textendash}96}, doi = {10.1016/j.jbi.2016.11.001}, url = {https://doi.org/10.1016/j.jbi.2016.11.001}, author = {Giorgos Poulis and Grigorios Loukides and Spiros Skiadopoulos and Aris Gkoulalas-Divanis} } @conference {DBLP:conf/ssdbm/AlGhamdiJSK17, title = {A Benchmark for Betweenness Centrality Approximation Algorithms on Large Graphs}, booktitle = {Proceedings of the 29th International Conference on Scientific and Statistical Database Management, Chicago, IL, USA, June 27-29, 2017}, year = {2017}, pages = {6:1{\textendash}6:12}, doi = {10.1145/3085504.3085510}, url = {https://doi.org/10.1145/3085504.3085510}, author = {Ziyad AlGhamdi and Fuad Jamour and Spiros Skiadopoulos and Panos Kalnis} } @article {DBLP:journals/bmcbi/ZagganasVPVSD17, title = {BUFET: boosting the unbiased miRNA functional enrichment analysis using bitsets}, journal = {BMC Bioinformatics}, volume = {18}, number = {1}, year = {2017}, pages = {399:1{\textendash}399:8}, doi = {10.1186/s12859-017-1812-8}, url = {https://doi.org/10.1186/s12859-017-1812-8}, author = {Konstantinos Zagganas and Thanasis Vergoulis and Maria D. Paraskevopoulou and Ioannis S. Vlachos and Spiros Skiadopoulos and Theodore Dalamagas} } @inbook {DBLP:reference/gis/Skiadopoulos17, title = {Directional Relations}, booktitle = {Encyclopedia of GIS.}, year = {2017}, pages = {476{\textendash}482}, doi = {10.1007/978-3-319-17885-1_1539}, url = {https://doi.org/10.1007/978-3-319-17885-1_1539}, author = {Spiros Skiadopoulos} } @book {DBLP:reference/gis/2017, title = {Encyclopedia of GIS}, year = {2017}, publisher = {Springer}, organization = {Springer}, isbn = {978-3-319-17884-4}, doi = {10.1007/978-3-319-17885-1}, url = {https://doi.org/10.1007/978-3-319-17885-1}, editor = {Shashi Shekhar and Hui Xiong and Xun Zhou} } @article {margaris-tldks, title = {Enhancing User Rating Database Consistency Through Pruning}, journal = {Transactions on Large-Scale Data- and Knowledge-Centered Systems XXXIV}, volume = {LNCS, volume 10620}, number = {Special issue on Consistency and Inconsistency in Data-centric Applications}, year = {2017}, pages = {33{\textendash}64}, publisher = {Springer Berlin Heidelberg}, abstract = {Recommender systems are based on information about users{\textquoteright} past behavior to formulate recommendations about their future actions. However, as time goes by the interests and likings of people may change: people listen to different singers or even different types of music, watch different types of movies, read different types of books and so on. Due to this type of changes, an amount of inconsistency is introduced in the database since a portion of it does not reflect the current preferences of the user, which is its intended purpose. In this paper, we present a pruning technique that removes old aged user behavior data from the ratings database, which are bound to correspond to invalidated preferences of the user. Through pruning (1) inconsistencies are removed and data quality is upgraded, (2) better rating prediction generation times are achieved and (3) the ratings database size is reduced. We also propose an algorithm for determining the amount of pruning that should be performed, allowing the tuning and operation of the pruning algorithm in an unsupervised fashion. The proposed technique is evaluated and compared against seven aging algorithms, which reduce the importance of aged ratings, and a state-of-the-art pruning algorithm, using datasets with varying characteristics. It is also validated using two distinct rating prediction computation strategies, namely collaborative filtering and matrix factorization. The proposed technique needs no extra information concerning the items{\textquoteright} characteristics (e.g. categories that they belong to or attributes{\textquoteright} values), can be used in all rating databases that include a timestamp and has been proved to be effective in any size of users-items database and under two rating prediction computation strategies. Note: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author{\textquoteright}s copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.}, keywords = {Collaborative filtering, Evaluation, Internet of Things, performance, Recommendation Applications, Social Networks, Web services}, doi = {10.1007/978-3-662-55947-5_3}, url = {https://link.springer.com/article/10.1007\%2Fs11761-017-0216-y}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {antoniouEuromed2017, title = {Experiences from the development of thematic itineraries in three Greek museums (Greek title: Εμπειρίες από την ανάπτυξη θεματικών διαδρομών σε τρία Ελληνικά μουσεία)}, booktitle = {Proceedings of the 2nd PanHellenic conference on Cultural Heritage (Euromed 2017)}, year = {2017}, month = {12}, abstract = {Private museums, as well as a considerable number of public regional museums, are confined by the small exhibition space and the relatively small number of exhibits and therefore cannot develop multiple exhibitions to satisfy visitors with different interests and characteristics. In this paper we report on our experieces from developing multiple thematic itineraries in the Tegea Folklore Museum , in the Cretan open-air museum "Lychnostatis" in Heraclion, and in the Panarcadic Archaeological Museum of Tripolis. The thematic itineraries in the Tegea Folklore Museum are (a) space (b) technology and (c) clothing. In the Cretan open-air museum "Lychnostatis", the itineraries are (a) natural sciences,(b) popular art, (c) pre-industrial technology and (d) folklore. In the Panarcadic Archaeological Museum of Tripolis we have the following itineraries: (a) appearance/clothing, (b) mortality, (c) nudity, (d) religion, (e) social status, (f) education, (g) healing practices and (h) everyday life. Each itinerary exploits a subset of the available exhibits to present a selected subject and is adapted to the needs of a predetermined and focused group of the general public. The results from the application of the approach, insofar, have shown that this is a promising path, both regarding the better exploitation of the space and the exhibits of the small museums, as well as regarding the better adaptation to the interests of the visitors.}, author = {Angela Antoniou and Costas Vassilakis and Manolis Wallace and Giorgos Lepouras and Vassilis Poulopoulos} } @article {margaris-soca-17, title = {Exploiting Internet of Things information to enhance venues{\textquoteright} recommendation accuracy}, journal = {Service Oriented Computing and Applications}, volume = {todb}, year = {2017}, month = {aug}, pages = {393{\textendash}409}, publisher = {Springer Nature}, abstract = {In this paper, we introduce a novel recommendation algorithm, which exploits data sourced from web services provided by the Internet of Things in order to produce more accurate venue recommendations. The proposed algorithm provides added value for the web services offered by the Internet of Things and enhances the state-of-the-art in this algorithm category by taking into account (a) web of things data regarding the contexts of the user and the context of the venues to be recommended (restaurants, movie theatres, etc.), such as the user{\textquoteright}s geographical position, road traffic and weather conditions, (b) qualitative aspects of the venues, such as price, atmosphere or service, (c) the semantic similarity of venues and (d) the influencing factors between social network users, derived from user participation in social networks. The combination of these features leads to more accurate and better user-targeted recommendations. We also present a framework which incorporates the above characteristics, and we evaluate the presented algorithm, both in terms of performance and recommendation quality.}, keywords = {collaborative filtering, Evaluation, Internet of Things, performance, Recommendation Applications, Social Networks, Web services}, doi = {10.1007/s11761-017-0216-y}, url = {https://link.springer.com/article/10.1007/s11761-017-0216-y}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {bourlakos-ikc17, title = {Formalization and visualization of the narrative for museum guides}, booktitle = {Proceedings of the third International KEYSTONE Conference (IKC2017)}, year = {2017}, month = {09}, publisher = {Springer}, organization = {Springer}, abstract = {There is a wide range of meta-data standards for the documentation of museum related information, such as CIDOC-CRM; these standards focus on the description of distinct exhibits. In contrast, there is a lack of standards for the digitization and documentation of the routes followed and information provided by museum guides. In this work we propose the notion of the narrative, which can be used to model a guided museum visit. We provide a formalization for the narrative so that it can be digitally encoded, and thus preserved, shared, re-used, further developed and exploited, and also propose an intuitive visualization approach.}, doi = {https://doi.org/10.1007/978-3-319-74497-1_1}, url = {https://link.springer.com/chapter/10.1007/978-3-319-74497-1_1}, author = {Ioannis Bourlakos and Manolis Wallace and Angela Antoniou and Costas Vassilakis and Giorgos Lepouras and Anna Vassiliki Karapanagiotou} } @conference {margaris-cbi17, title = {Improving Collaborative Filtering{\textquoteright}s Rating Prediction Quality by Considering Shifts in Rating Practices}, booktitle = {Proceedings of the 19th IEEE International Conference on business informatics (CBI17)}, year = {2017}, month = {07}, publisher = {IEEE}, organization = {IEEE}, abstract = {Users that populate ratings databases, such as IMDB, follow different marking practices, in the sense that some are stricter, while others are more lenient. This aspect has been captured by the most widely used similarity metrics in collaborative filtering, namely the Pearson Correlation and the Adjusted Cosine Similarity, which adjust each individual rating by the mean of the ratings entered by the specific user, when computing similarities. However, relying on the mean value presumes that the users{\textquoteright} marking practices remain constant over time; in practice though, it is possible that a user{\textquoteright}s marking practices change over time, i.e. a user could start as strict and subsequently become lenient, or vice versa. In this work, we propose an approach to take into account marking practices shifts by (1) introducing the concept of dynamic user rating averages which follow the users{\textquoteright} marking practices shifts, (2) presenting two alternative algorithms for computing a user{\textquoteright}s dynamic averages and (3) performing a comparative evaluation among these two algorithms and the classic static average (unique mean value) that the Pearson Correlation uses.}, doi = {10.1109/CBI.2017.24}, url = {https://ieeexplore.ieee.org/abstract/document/8010718/}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {margaris-iscc17, title = {Improving Collaborative Filtering{\textquoteright}s Rating Prediction Quality in Dense Datasets, by Pruning Old Ratings}, booktitle = {Proceedings of the 22nd IEEE Symposium on Computers and Communications (ISCC17)}, year = {2017}, month = {07}, publisher = {IEEE}, organization = {IEEE}, abstract = {In this paper, we introduce a pruning algorithm which removes aged user ratings from the rating database used by collaborative filtering algorithms, in order to (1) improve prediction quality and (2) minimize the rating database size, as well as the rating prediction generation time. The proposed algorithm needs no extra information concerning the items{\textquoteright} characteristics (e.g. categories that they belong to or attributes{\textquoteright} values) and can be used with all rating databases that include a timestamp. Furthermore, we propose and validate a method for identifying the most prominent combination of a pruning algorithm and a pruning level for datasets, allowing thus to perform the selection of pruning algorithm and pruning level in an unsupervised fashion.}, doi = {10.1109/ISCC.2017.8024683}, url = {https://ieeexplore.ieee.org/document/8024683/}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {DBLP:conf/gis/Chatzigeorgakidis17, title = {Indexing Geolocated Time Series Data}, booktitle = {Proceedings of the 25th ACM SIGSPATIAL International Conference on Advances in Geographic Information Systems, GIS 2017, Redondo Beach, CA, USA, November 7-10, 2017}, year = {2017}, pages = {19:1{\textendash}19:10}, doi = {10.1145/3139958.3140003}, url = {https://doi.org/10.1145/3139958.3140003}, author = {Georgios Chatzigeorgakidis and Dimitrios Skoutas and Kostas Patroumpas and Spiros Athanasiou and Spiros Skiadopoulos} } @inbook {marg16d, title = {Knowledge-Based Leisure Time Recommendations in Social Networks}, booktitle = {Current Trends on Knowledge-Based Systems}, series = {Intelligent Systems Reference Library}, year = {2017}, pages = {23{\textendash}48}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, chapter = {Knowledge-Based Leisure Time Recommendations in Social Networks}, abstract = {We introduce a novel knowledge-based recommendation algorithm for leisure time information to be used in social networks, which enhances the state-of-the-art in this algorithm category by taking into account (a) qualitative aspects of the recommended places (restaurants, museums, tourist attractions etc.), such as price, service and atmosphere, (b) influencing factors between social network users, (c) the semantic and geographical distance between locations and (d) the semantic categorization of the places to be recommended. The combination of these features leads to more accurate and better user-targeted leisure time recommendations.}, keywords = {Attribute constraints, collaborative filtering, Knowledge-based Recommender Systems, Semantic Information, Social Networks}, doi = {10.1007/978-3-319-51905-0_2}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis}, editor = {Giner Alor Hernandez and Rafael Valencia Garcia} } @article {DBLP:journals/tkde/TerrovitisPMS17, title = {Local Suppression and Splitting Techniques for Privacy Preserving Publication of Trajectories}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {29}, number = {7}, year = {2017}, pages = {1466{\textendash}1479}, doi = {10.1109/TKDE.2017.2675420}, url = {https://doi.org/10.1109/TKDE.2017.2675420}, author = {Manolis Terrovitis and Giorgos Poulis and Nikos Mamoulis and Spiros Skiadopoulos} } @conference {boukoros2017, title = {Modeling Server Workloads for Campus Email Traffic Using Recurrent Neural Networks}, booktitle = {Proceedings of the 24th International Conference on Neural Information Processing (ICONIP 2017)}, year = {2017}, pages = {57{\textendash}66}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {As email workloads keep rising, email servers need to handle this explosive growth while offering good quality of service to users. In this work, we focus on modeling the workload of the email servers of four universities (2 from Greece, 1 from the UK, 1 from Australia). We model all types of email traffic, including us-er and system emails, as well as spam. We initially tested some of the most popu-lar distributions for workload characterization and used statistical tests to evaluate our findings. The significant differences in the prediction accuracy results for the four datasets led us to investigate the use of a Recurrent Neural Network (RNN) as time series modeling to model the server workload, which is a first for such a problem. Our results show that the use of RNN modeling leads in most cases to high modeling accuracy for all four campus email traffic datasets.}, keywords = {Email traffic, Model server workload, Recurrent neural network, Time series modeling}, doi = {10.1007/978-3-319-70139-4_6}, author = {Spyros Boukoros and Anupiya Nugaliyadde and Angelos Marnerides and Costas Vassilakis and Polychronis Koutsakis and Kok Wai Wong} } @conference {theodorakopoulos-smap2017, title = {Personalized Augmented Reality Experiences in Museums using Google Cardboards}, booktitle = {2017 12th International Workshop on Semantic and Social Media Adaptation and Personalization (SMAP)}, year = {2017}, month = {07}, publisher = {IEEE CPS}, organization = {IEEE CPS}, abstract = {In this short paper we examine the suitability of the Google Cardboard as a means for the delivery of personalized cultural experiences. Specifically, we develop the content and create the application required in order to provide highly personalized visits to the Archaeological Museum in Tripolis, Greece. We also examine the usability issues related to the use of Google Cardboards. Early results are promising, and based on them we also outline the next steps ahead.}, doi = {10.1109/smap.2017.8022676}, url = {https://ieeexplore.ieee.org/document/8022676/}, author = {Marinos Theodorakopoulos and Nikos Papageorgopoulos and Andriana Mourti and Angela Antoniou and Manolis Wallace and Giorgos Lepouras and Costas Vassilakis and Nikos Platis} } @proceedings {DBLP:conf/gis/2017, title = {Proceedings of the 25th ACM SIGSPATIAL International Conference on Advances in Geographic Information Systems, GIS 2017, Redondo Beach, CA, USA, November 7-10, 2017}, year = {2017}, publisher = {ACM}, isbn = {978-1-4503-5490-5}, url = {http://dl.acm.org/citation.cfm?id=3139958}, editor = {Erik G. Hoel and Shawn D. Newsam and Siva Ravada and Roberto Tamassia and Goce Trajcevski} } @proceedings {DBLP:conf/ssdbm/2017, title = {Proceedings of the 29th International Conference on Scientific and Statistical Database Management, Chicago, IL, USA, June 27-29, 2017}, year = {2017}, publisher = {ACM}, isbn = {978-1-4503-5282-6}, doi = {10.1145/3085504}, url = {https://doi.org/10.1145/3085504} } @article {marg2017a-fgcs, title = {Query personalization using social network information and collaborative filtering techniques}, journal = {Future Generation of Computer Systems}, volume = {Special Issue on Recommender Systems for Large-Scale Social Networks}, year = {2017}, month = {jan}, pages = {440{\textendash}450}, abstract = {Query personalization has emerged as a means to handle the issue of information volume growth, aiming to tailor query answer results to match the goals and interests of each user. Query personalization dynamically enhances queries, based on information regarding user preferences or other contextual information; typically enhancements relate to incorporation of conditions that filter out results that are deemed of low value to the user and/or ordering results so that data of high value are presented first. In the domain of personalization, social network information can prove valuable; users{\textquoteright} social networks profiles, including their interests, influence from social friends, etc. can be exploited to personalize queries. In this paper, we present a query personalization algorithm, which employs collaborative filtering techniques and takes into account influence factors between social network users, leading to personalized results that are better-targeted to the user.}, doi = {10.1016/j.future.2017.03.015}, url = {http://www.sciencedirect.com/science/article/pii/S0167739X17303692}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @article {581, title = {Query Reorganisation Algorithms for Efficient Boolean Information Filtering}, journal = {IEEE Transactions on Knowledge and Data Engineering}, volume = {29}, year = {2017}, pages = {418{\textendash}432}, abstract = {In the information filtering paradigm, clients subscribe to a server with continuous queries that express their information needs and get notified every time appropriate information is published. To perform this task in an efficient way, servers employ indexing schemes that support fast matches of the incoming information with the query database. Such indexing schemes involve (i) main-memory trie-based data structures that cluster similar queries by capturing common elements between them and (ii) efficient filtering mechanisms that exploit this clustering to achieve high throughput and low filtering times. However, state-of-the-art indexing schemes are sensitive to the query insertion order and cannot adopt to an evolving query workload, degrading the filtering performance over time. In this paper, we present an adaptive trie-based algorithm that outperforms current methods by relying on query statistics to reorganise the query database. Contrary to previous approaches, we show that the nature of the constructed tries, rather than their compactness, is the determining factor for efficient filtering performance. Our algorithm does not depend on the order of insertion of queries in the database, manages to cluster queries even when clustering possibilities are limited, and achieves more than 96\% filtering time improvement over its state-of-the-art competitors. Finally, we demonstrate that our solution is easily extensible to multi-core machines.}, keywords = {dissemination, indexing methods, Information filtering, user profiles and alert services}, doi = {10.1109/TKDE.2016.2620140}, url = {https://doi.org/10.1109/TKDE.2016.2620140}, author = {Lefteris Zervakis and Christos Tryfonopoulos and Spiros Skiadopoulos and Manolis Koubarakis} } @article {vassilakis-snam-2017a, title = {Stimulation of reflection and discussion in museum visits through the use of social media}, journal = {Social Network Analysis and Mining}, volume = {7}, number = {40}, year = {2017}, month = {12}, pages = {1-12}, publisher = {Springer-Verlag GmbH Austria}, abstract = {In this paper, we examine how social media can be linked to cultural heritage and in particular how we can incorporate games, social networks, history reflection and culture. More specifically, we explore the following aspects: (a) how social media sites can be integrated into the museum user experience (b) how user interactions within the social media, both within the context of the museum experience and outside it, can be exploited to enhance the quality of recommendations made to the users, (c) how trending topics from social media can be used to link museum exhibits with today{\textquoteright}s topics of interest and (d) how multi-level related terms extraction from social media data can lead to proposals for reflections to users. The end goal is to provide increased stimuli for users to study exhibits deeper and reflect on them, as well as to trigger discussion between the users, thus maximizing the impact of a museum visit.}, keywords = {big data, cognitive style, Communication, reflection, Social Networks, user profiling}, doi = {10.1007/s13278-017-0460-3}, url = {https://link.springer.com/article/10.1007/s13278-017-0460-3}, author = {Costas Vassilakis and Angela Antoniou and Giorgos Lepouras and Vassilis Poulopoulos and Manolis Wallace and Stavroula Bampatzia and Ioannis Bourlakos} } @article {margaris-csimq-2017, title = {Using Time Clusters for Following Users{\textquoteright} Shifts in Rating Practices}, journal = {Complex Systems Informatics and Modeling Quarterly}, volume = {13}, year = {2017}, abstract = {Users that enter ratings for items follow different rating practices, in the sense that, when rating items, some users are more lenient, while others are stricter. This aspect is taken into account by the most widely used similarity metric in user-user collaborative filtering, namely, the Pearson Correlation, which adjusts each individual user rating by the mean value of the ratings entered by the specific user, when computing similarities. However, a user{\textquoteright}s rating practices change over time, i.e. a user could start as strict and subsequently become lenient or vice versa. In that sense, the practice of using a single mean value for adjusting users{\textquoteright} ratings is inadequate, since it fails to follow such shifts in users{\textquoteright} rating practices, leading to decreased rating prediction accuracy. In this work, we address this issue by using the concept of dynamic averages introduced earlier and we extend earlier work by (1) introducing the concept of rating time clusters and (2) presenting a novel algorithm for calculating dynamic user averages and exploiting them in user-user collaborative, filtering implementations. The proposed algorithm incorporates the aforementioned concept and is able to follow more successfully shifts in users{\textquoteright} rating practices. It has been evaluated using numerous datasets, and has been found to introduce significant gains in rating prediction accuracy, while outperforming the dynamic average computation approaches that are presented earlier.}, keywords = {collaborative filtering, Dynamic Average, Rating Abstention Interval, Rating Time Clusters, Ratings{\textquoteright} Timestamps, Recommender Systems}, issn = {2255-9922}, doi = {10.7250/csimq.2017-13.02}, author = {Dionisis Margaris and Costas Vassilakis} } @conference {591, title = {A crawler architecture for harvesting the clear, social, and dark web for IoT-related cyber-threat intelligence}, booktitle = {In Proceedings of the IEEE Workshop on Cyber Security \& Resilience in the Internet of Things (CSRIoT @ IEEE Services)}, year = {2016}, month = {July 2016}, publisher = {IEEE}, organization = {IEEE}, address = {Milan, Italy}, abstract = {The clear, social, and dark web have lately been identified as rich sources of valuable cyber-security information that {\textendash}given the appropriate tools and methods{\textendash} may be identified, crawled and subsequently leveraged to actionable cyber- threat intelligence. In this work, we focus on the information gathering task, and present a novel crawling architecture for transparently harvesting data from security websites in the clear web, security forums in the social web, and hacker fo- rums/marketplaces in the dark web. The proposed architecture adopts a two-phase approach to data harvesting. Initially a machine learning-based crawler is used to direct the harvesting towards websites of interest, while in the second phase state- of-the-art statistical language modelling techniques are used to represent the harvested information in a latent low-dimensional feature space and rank it based on its potential relevance to the task at hand. The proposed architecture is realised using exclusively open-source tools, and a preliminary evaluation with crowdsourced results demonstrates its effectiveness.}, keywords = {crawling architecture, cyber-security, cyber-threat intelligence, IoT, language models, Machine Learning}, url = {http://users.uop.gr/ trifon/papers/pdf/csriot19-KCTS.pdf}, author = {Paris Koloveas and Thanasis Chantzios and Christos Tryfonopoulos and Spiros Skiadopoulos} } @conference {DBLP:conf/esws/ZervakisTSK16, title = {Full-Text Support for Publish/Subscribe Ontology Systems}, booktitle = {The Semantic Web. Latest Advances and New Domains - 13th International Conference, ESWC 2016, Heraklion, Crete, Greece, May 29 - June 2, 2016, Proceedings}, year = {2016}, pages = {233{\textendash}249}, doi = {10.1007/978-3-319-34129-3_15}, url = {https://doi.org/10.1007/978-3-319-34129-3_15}, author = {Lefteris Zervakis and Christos Tryfonopoulos and Spiros Skiadopoulos and Manolis Koubarakis} } @conference {margaris2016a, title = {Improving QoS Delivered by WS-BPEL Scenario Adaptation through Service Execution Parallelization}, booktitle = {Proceedings of the 31st Annual ACM Symposium on Applied Computing}, year = {2016}, pages = {1590-1596}, publisher = {ACM}, organization = {ACM}, abstract = {WS-BPEL scenario execution adaptation has been proposed by researchers as a response to the need of users to tailor the WS-BPEL scenario execution to their individual preferences; these preferences are typically expressed through Quality of Service (QoS) policies, which the adaptation mechanism considers in order to select the services that will ultimately be invoked to realize the desired business process. In this paper, we study the potential to parallelize the execution of the WS-BPEL scenario in order to minimize its response time and/or achieving higher scores in the other qualitative dimensions, such as cost, reliability, etc., at the same time. We also describe, develop and validate a parallelization algorithm for realizing the proposed enhancements.}, doi = {10.1145/2851613.2851805}, url = {https://dl.acm.org/citation.cfm?id=2851805}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @conference {vas-euromed16, title = {Interconnecting Objects, Visitors, Sites and (Hi)Stories Across Cultural and Historical Concepts: The CrossCult Project}, booktitle = {Digital Heritage. Progress in Cultural Heritage: Documentation, Preservation, and Protection}, year = {2016}, month = {10}, pages = {501{\textendash}510}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, abstract = {Human History, is a huge mesh of interrelated facts and concepts, spanning beyond borders, encompassing global aspects and finally constituting a shared, global experience. This is especially the case regarding European history, which is highly interconnected by nature; however, most History-related experiences that are today offered to the greater public, from schools to museums, are siloed. The CrossCult project aims to provide the means for offering citizens and cultural venue visitors a more holistic view of history, in the light of cross-border interconnections among pieces of cultural heritage, other citizens viewpoints and physical venues. To this end, the CrossCult project will built a comprehensive knowledge base encompassing information and semantic relationships across cultural information elements, and will provide the technological means for delivering the contents of this knowledge base to citizens and venue visitors in a highly personalized manner, creating narratives for the interactive experiences that maximise situational curiosity and serendipitous learning. The CrossCult platform will also exploit the cognitive/emotional profiles of the participants as well as temporal, spatial and miscellaneous features of context, including holidays and anniversaries, social media trending topics and so forth.}, doi = {10.1007/978-3-319-48496-9_39}, url = {http://link.springer.com/chapter/10.1007/978-3-319-48496-9_39}, author = {Costas Vassilakis and Angela Antoniou and Giorgos Lepouras and Manolis Wallace and Ioanna Lykourentzou and Y. Naudet} } @proceedings {DBLP:conf/edbt/2016w, title = {Proceedings of the Workshops of the EDBT/ICDT 2016 Joint Conference, EDBT/ICDT Workshops 2016, Bordeaux, France, March 15, 2016}, volume = {1558}, year = {2016}, publisher = {CEUR-WS.org}, url = {http://ceur-ws.org/Vol-1558}, editor = {Themis Palpanas and Kostas Stefanidis} } @conference {marg2016-ssci, title = {Pruning and Aging for User Histories in Collaborative Filtering}, booktitle = {Proceedings of the 2016 IEEE Symposium Series on Computational Intelligence}, year = {2016}, month = {12}, abstract = {In this paper, we introduce algorithms for pruning and aging user ratings in collaborative filtering systems, based on their oldness, under the rationale that aged user ratings may not accurately reflect the current state of users regarding their preferences. The aging algorithm reduces the importance of aged ratings, while the pruning algorithm removes them from the database. The algorithms are evaluated against various types of datasets. The pruning algorithm has been found to present a number of advantages, namely (1) reducing the rating database size, (2) achieving better prediction generation times and (3) improving prediction quality by cutting off predictions with high error. The algorithm can be used in all rating databases that include a timestamp and has been proved to be effective in any type of dataset, from movies and music, to videogames and books.}, doi = {10.1109/ssci.2016.7849920}, url = {https://ieeexplore.ieee.org/document/7849920/}, author = {Dionisis Margaris and Costas Vassilakis} } @article {Margaris_2016, title = {Recommendation information diffusion in social networks considering user influence and semantics}, journal = {Social Network Analysis and Mining}, volume = {6}, number = {1}, year = {2016}, month = {nov}, pages = {108}, publisher = {Springer Nature}, abstract = {One of the major problems in the domain of social networks is the handling and diffusion of the vast, dynamic and disparate information created by its users. In this context, the information contributed by users can be exploited to generate recommendations for other users. Relevant recommender systems take into account static data from users{\textquoteright} profiles, such as location, age or gender, complemented with dynamic aspects stemming from the user behavior and/or social network state such as user preferences, items{\textquoteright} general acceptance and influence from social friends. In this paper, we enhance recommendation algorithms used in social networks by taking into account qualitative aspects of the recommended items, such as price and reliability, the influencing factors between social network users, the social network user behavior regarding their purchases in different item categories and the semantic categorization of the products to be recommended. The inclusion of these aspects leads to more accurate recommendations and diffusion of better user-targeted information. This allows for better exploitation of the limited recommendation space, and therefore online advertisement efficiency is raised.}, keywords = {Collaborative filtering, Information diffusion, Quality of service, Semantic Information, Social Networks}, doi = {10.1007/s13278-016-0416-z}, url = {http://rdcu.be/mZ7e}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @conference {575, title = {R-Susceptibility: An IR-Centric Approach to Assessing Privacy Risks for Users in Online Communities}, booktitle = {Proceedings of the 39th Annual International ACM SIGIR Conference}, year = {2016}, month = {July}, address = {Pisa, Italy}, author = {Joanna Asia Biega and Krishna P. Gummadi and Ida Mele and Dragan Milchevski and Christos Tryfonopoulos and Gerhard Weikum} } @proceedings {DBLP:conf/esws/2016, title = {The Semantic Web. Latest Advances and New Domains - 13th International Conference, ESWC 2016, Heraklion, Crete, Greece, May 29 - June 2, 2016, Proceedings}, volume = {9678}, year = {2016}, publisher = {Springer}, isbn = {978-3-319-34128-6}, doi = {10.1007/978-3-319-34129-3}, url = {https://doi.org/10.1007/978-3-319-34129-3}, editor = {Harald Sack and Eva Blomqvist and Mathieu d{\textquoteright}Aquin and Chiara Ghidini and Simone Paolo Ponzetto and Christoph Lange} } @conference {bampatzia-gala2016, title = {Serious games: Valuable Tools for Cultural Heritage}, booktitle = {Proceedings of the 2016 Games and Learning Alliance Conference}, year = {2016}, month = {12}, pages = {331{\textendash}341}, abstract = {Wishing to connect cultural heritage, games and social networks, the present work describes games to be used within the framework of a European H2020 project. For the purposes of supporting the museum visit, before, during and after, 5 games were designed for social networks to accomplish user profil-ing, to promote the museum and the application through social network dissemi-nation, to introduce museum items and themes and to also function as visit sou-venirs. The games are also presented in a generic framework for games in cultural heritage, which has been used successfully in the past.}, doi = {https://doi.org/10.1007/978-3-319-50182-6_30}, url = {https://link.springer.com/chapter/10.1007/978-3-319-50182-6_30}, author = {Stavroula Bampatzia and Ioannis Bourlakos and Angela Antoniou and Costas Vassilakis and Giorgos Lepouras and Manolis Wallace} } @conference {DBLP:conf/edbt/ZervakisTSSS16, title = {Towards Publish/Subscribe Functionality on Graphs}, booktitle = {Proceedings of the Workshops of the EDBT/ICDT 2016 Joint Conference, EDBT/ICDT Workshops 2016, Bordeaux, France, March 15, 2016.}, year = {2016}, url = {http://ceur-ws.org/Vol-1558/paper13.pdf}, author = {Lefteris Zervakis and Christos Tryfonopoulos and Vinay Setty and Stephan Seufert and Spiros Skiadopoulos} } @conference {bampatzia2016a, title = {The use of semantics in the CrossCult H2020 project}, booktitle = {Proceedings of the second International KEYSTONE Conference, (IKC2016)}, year = {2016}, pages = {190{\textendash}195}, abstract = {CrossCult is a newly started project that aims to make reflective history a reality in the European cultural context. In this paper we examine how the project aims to take advantage of advances in semantic technologies in order to achieve its goals. Specifically, we see what the quest for reflection is and, through practical examples from two of the project{\textquoteright}s flagship pilots, explain how semantics can assist in this direction}, doi = {https://doi.org/10.1007/978-3-319-53640-8_17}, url = {https://link.springer.com/chapter/10.1007/978-3-319-53640-8_17}, author = {Stavroula Bampatzia and Omar Gustavo Bravo-Quezada and Angela Antoniou and Martin Lopez Nores and Manolis Wallace and Giorgos Lepouras and Costas Vassilakis} } @conference {bampatzia-smap16, title = {Using Social media to stimulate history reflection in cultural heritage}, booktitle = {Proceedings of Semantic and Social Media Adaptation and Personalization (SMAP) 2016}, year = {2016}, month = {10}, abstract = {CrossCult H2020 is a European project, the aim of which is the reflection of history in a cultural setting. In this paper, we describe how social media can be linked to cultural heritage and in particular how we can incorporate games, social networks, history reflection and culture. The paper presents the case study of one of the project pilots, to show how history reflection can be enhanced with the use of social networks.}, doi = {10.1109/SMAP.2016.7753390}, url = {https://ieeexplore.ieee.org/document/7753390/}, author = {Stavroula Bampatzia and Angela Antoniou and Giorgos Lepouras and Costas Vassilakis and Manolis Wallace} } @proceedings {DBLP:conf/bigdataconf/2015, title = {2015 IEEE International Conference on Big Data, Big Data 2015, Santa Clara, CA, USA, October 29 - November 1, 2015}, year = {2015}, publisher = {IEEE Computer Society}, isbn = {978-1-4799-9926-2}, url = {http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=7347101} } @conference {DBLP:conf/kcap/TsafaraTSZ15, title = {Cloud-Based Data and Knowledge Management for Multi-Centre Biomedical Studies}, booktitle = {Proceedings of the 8th International Conference on Knowledge Capture, K-CAP 2015, Palisades, NY, USA, October 7-10, 2015}, year = {2015}, pages = {24:1{\textendash}24:4}, doi = {10.1145/2815833.2816949}, url = {https://doi.org/10.1145/2815833.2816949}, author = {Amalia Tsafara and Christos Tryfonopoulos and Spiros Skiadopoulos and Lefteris Zervakis} } @conference {563, title = {Cloud-Based Data and Knowledge Management for Multi-Centre Biomedical Studies}, booktitle = {Proceedings of the International Conference on Knowledge Capture (K-CAP)}, year = {2015}, month = {October 7-10}, address = {Palisades NY, USA}, abstract = {Among the basic research tools for (bio)medical science are epidemiological studies that typically involve a number of hospitals, clinics, and research centres scattered around the world, and are often referred to as multi-centre studies. Clearly, the effectiveness and importance of a multi-centre study increases with the number of participating centres and enrolled patients, but at the same time this natural distribution in the production of research data requires sophisticated data management infrastructures to support the participating units. This kind of infrastructure is not only expensive to build and maintain, but also cannot be reused as it is often tailored to a specific study. In this work, we present a cloud-based system, coined CLOUDSTUDY, that allows users without any computer science background to design, deploy, and administer platforms aimed for managing, sharing, and analysing clinical data from multi-centre studies. The CLOUDSTUDY system provides a zero-administration, zero-cost online tool for creating multi- centre studies that (i) enhances re-usability by introducing study templates, (ii) supports (bio)medical needs through specialised data types, and (iii) emphasises data filtering/export through an expressive yet simple graphical query engine.}, doi = {10.1145/2815833.2816949}, url = {https://doi.org/10.1145/2815833.2816949}, author = {Amalia Tsafara and Christos Tryfonopoulos and Spiros Skiadopoulos and Lefteris Zervakis} } @conference {marg15a, title = {A Collaborative Filtering Algorithm with Clustering for Personalized Web Service Selection in Business Processes}, booktitle = {Proceedings of RCIS 2015}, year = {2015}, month = {5}, abstract = {Recommender systems aim to propose items that are expected to be of interest to the users. As one of the most successful approaches to building recommender systems, collaborative filtering exploits the known preferences of a group of users to formulate recommendations or predictions of the unknown preferences for other users. In many cases, collaborative filtering algorithms handle complex items, which are described using hierarchical tree structures containing rich semantic information. In order to make accurate recommendations on such items, the related algorithms must examine all aspects of the available semantic information. Thus, when collaborative filtering techniques are employed to adapt the execution of business processes, they must take into account the services{\textquoteright} Quality of Service parameters, so as to generate recommendations tailored to the individual user needs. In this paper, we present a collaborative filtering-based algorithm which takes into account the web services{\textquoteright} QoS parameters in order to tailor the execution of business processes to the preferences of users. An offline clustering technique is also introduced for supporting the efficient and scalable execution of proposed algorithm under the presence of large repositories of sparse data.}, keywords = {business processes, clustering, collaborative filtering, hierarchical tree, performance, Quality of service, Web services}, doi = {10.1109/RCIS.2015.7128877}, author = {Dionisis Margaris and P. Georgiadis and Costas Vassilakis} } @conference {570, title = {Constructing Subsumption Hierarchies of Web Queries}, booktitle = {Proceedings of the International Workshop on Dataset PROFIling and fEderated Search for Linked Data (PROFILES @ ESWC)}, year = {2015}, month = {May}, address = {Portoroz, Slovenia}, author = {Alexander Prohaska and Christos Tryfonopoulos and Georgiana Ifrim} } @article {katifori15a, title = {Effectiveness of visualization for information retrieval through ontologies with entity evolution: the impact of ontology modeling}, journal = {International Journal of Information Retrieval Research}, volume = {5}, number = {2}, year = {2015}, pages = {26}, abstract = {Incorporating digital tools in the business and scientific research workflows is at the moment an on-going process, challenging and demanding as every domain has its own needs in terms of data models and information retrieval methods. The information in some domains involves entity evolution, a characteristic that introduces additional tasks, such as finding all evolution stages of an entity, and poses additional requirements for the information retrieval process. In this paper, we present a user study aiming to investigate how the different aspects of ontology modelling affect the performance and effectiveness of users regarding information retrieval tasks that are carried out using visualization methods. The results of the user study are analyzed and guidelines for ontology design are offered.}, doi = {10.4018/IJIRR.2015040104}, author = {Akrivi Katifori and Costas Vassilakis and Giorgos Lepouras and Elena Torou} } @conference {margaris2015a, title = {A Hybrid Framework for WS-BPEL Scenario Execution Adaptation, Using Monitoring and Feedback Data}, booktitle = {Proceedings of the 30th ACM/SIGAPP Symposium On Applied Computing, SOAP track}, year = {2015}, month = {4}, publisher = {ACM}, organization = {ACM}, abstract = {In this paper, we present a framework which provides runtime adaptation for BPEL scenarios. The adaptation is based on (a) quality of service parameters of available web services (b) quality of service policies specified by users (c) collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, (d) monitoring, in order to follow the variations of QoS attribute values and (e) on users{\textquoteright} opinions services they have used.}, doi = {10.1145/2695664.2695687}, url = {https://dl.acm.org/citation.cfm?doid=2695664.2695687}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @article {margaris14a, title = {An integrated framework for adapting WS-BPEL scenario execution using QoS and collaborative filtering techniques}, journal = {Science of Computer Programming}, volume = {98}, year = {2015}, pages = {707{\textendash}734}, abstract = {In this paper, we present a framework which incorporates runtime adaptation for BPEL scenarios. The adaptation is based on (a) the quality of service parameters of available services, allowing for tailoring their execution to the diverse needs of individual users and (b)collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, in the context of the same business processes. The proposed framework also caters maintaining the transactional semantics that invocations to multiple services offered by the same provider may bear.}, doi = {10.1016/j.scico.2014.10.007}, url = {http://www.sciencedirect.com/science/article/pii/S0167642314004778}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @conference {DBLP:conf/bigdataconf/Chatzigeorgakidis15, title = {A MapReduce based k-NN joins probabilistic classifier}, booktitle = {2015 IEEE International Conference on Big Data, Big Data 2015, Santa Clara, CA, USA, October 29 - November 1, 2015}, year = {2015}, pages = {952{\textendash}957}, doi = {10.1109/BigData.2015.7363844}, url = {https://doi.org/10.1109/BigData.2015.7363844}, author = {Georgios Chatzigeorgakidis and Sophia Karagiorgou and Spiros Athanasiou and Spiros Skiadopoulos} } @book {DBLP:books/sp/GL2015, title = {Medical Data Privacy Handbook}, year = {2015}, publisher = {Springer}, organization = {Springer}, isbn = {978-3-319-23632-2}, doi = {10.1007/978-3-319-23633-9}, url = {https://doi.org/10.1007/978-3-319-23633-9}, editor = {Aris Gkoulalas-Divanis and Grigorios Loukides} } @conference {kmas15, title = {A mobile-enabled platform for presenting and disseminating cultural heritage information enhanced with augmented reality (Greek title: ΜΙΑ ΠΛΑΤΦΟΡΜΑ ΓΙΑ ΠΑΡΟΥΣΙΑΣΗ ΚΑΙ ΔΙΑΧΥΣΗ ΠΛΗΡΟΦΟΡΙΩΝ ΠΟΛΙΤΙΣΤΙΚΗΣ ΚΛΗΡΟΝΟΜΙΑΣ ΜΕ ΥΠΟΣΤΗΡΙΞΗ ΓΙΑ ΚΙΝΗΤΕΣ ΣΥΣΚΕΥΕΣ ΚΑΙ ΕΜΠ}, booktitle = {1st Panhellenic Conference on Cultural Heritage Digitization}, year = {2015}, month = {9}, abstract = {The advent of mobile technologies has created opportunities for more effective delivery of cultural heritage information to all interested parties, and especially tourists who are on-the-move. Many people nowadays are equipped with smartphones or tablets equipped with location tracking devices such as GPS and compasses and having internet access available; these smartphones can be used for efficient delivery of cultural heritage information, in a personalized and timely fashion. Moreover, the computing resources of these smartphones are adequate to enable the use of augmented reality techniques, which provide a lively and engaging experience to the users. However, the same content still needs to be disseminated to users of stationary computers. In this paper, we report on the design and development of a mobile-enabled platform for presenting and disseminating cultural heritage information enhanced with augmented reality and integration with social networks.}, author = {K. Μασσέλος and Costas Vassilakis and Giorgos Lepouras and Christos Tryfonopoulos and Ν. Τσελίκας and Nikos Platis} } @conference {556, title = {A Platform for the Presentation and Dissemination of Cultural Heritage Information for Mobile Devices Enriched with Augmented Reality}, booktitle = {Proceedings of the Greek Conference for the Digitization of Cultural Information (EUROMED)}, year = {2015}, month = {September}, address = {Volos, Greece}, author = {K. Masselos and Costas Vassilakis and Giorgos Lepouras and Christos Tryfonopoulos and N. Tselikas and N. Platis} } @proceedings {DBLP:conf/kcap/2015, title = {Proceedings of the 8th International Conference on Knowledge Capture, K-CAP 2015, Palisades, NY, USA, October 7-10, 2015}, year = {2015}, publisher = {ACM}, isbn = {978-1-4503-3849-3}, doi = {10.1145/2815833}, url = {https://doi.org/10.1145/2815833}, editor = {Ken Barker and Jos{\'e} Manu{\'e}l G{\'o}mez-P{\'e}rez} } @conference {aamas15-GPT, title = {PViz: Visualising P2P Multi-Agent Simulations}, booktitle = {Proceedings of the International Conference on Autonomous Agents and Multiagent Systems (AAMAS)}, year = {2015}, month = {May}, pages = {1945{\textendash}1946}, address = {Istanbul, Turkey}, author = {Dimitris Giouroukis and Nikos Platis and Christos Tryfonopoulos} } @conference {margaris15c, title = {On Replacement Service Selection in WS-BPEL Scenario Adaptation}, booktitle = {Proceedings of the 8th IEEE International Conference on Service Oriented Computing \& Applications (SOCA 2015)}, year = {2015}, month = {9}, publisher = {IEEE}, organization = {IEEE}, abstract = {WS-BPEL scenario execution adaptation has been proposed by numerous researchers as a response to the need of users to tailor the WS-BPEL scenario execution to their individual preferences; these preferences are typically expressed through Quality of Service (QoS) policies, which the adaptation mechanism considers in order to select the services that will ultimately be invoked to realize the desired business process. In this paper, we consider a number of issues related to WS-BPEL scenario adaptation, aiming to enhance adaptation quality and improve the QoS offered to end users. More specifically, with the goal of broadening the service selection pool we (a) discuss the identification of potential services that can be used to realize a functionality used in the WS-BPEL scenario and (b) elaborate on transactional semantics that invocations to multiple services offered by the same provider may bear. We also describe and validate an architecture for realizing the proposed enhancements.}, doi = {10.1109/SOCA.2015.11}, author = {Dionisis Margaris and P. Georgiadis and Costas Vassilakis} } @inbook {565, title = {SECRETA: A Tool for Anonymizing Relational, Transaction and RT-Datasets}, booktitle = {Medical Data Privacy Handbook}, year = {2015}, pages = {83-109}, publisher = {Springer}, organization = {Springer}, author = {Giorgos Poulis and Aris Gkoulalas-Divanis and Grigorios Loukides and Spiros Skiadopoulos and Christos Tryfonopoulos}, editor = {Aris Gkoulalas-Divanis and Grigorios Loukides} } @inbook {DBLP:books/sp/15/PoulisGLST15, title = {SECRETA: A Tool for Anonymizing Relational, Transaction and RT-Datasets}, booktitle = {Medical Data Privacy Handbook}, year = {2015}, pages = {83{\textendash}109}, doi = {10.1007/978-3-319-23633-9_5}, url = {https://doi.org/10.1007/978-3-319-23633-9_5}, author = {Giorgos Poulis and Aris Gkoulalas-Divanis and Grigorios Loukides and Spiros Skiadopoulos and Christos Tryfonopoulos} } @conference {541, title = {Towards Content-Based Publish/Subscribe for Distributed Social Networks}, booktitle = {Proceedings of the International Conference on Distributed Event-Based Systems (DEBS)}, year = {2015}, month = {June}, address = {Oslo, Norway}, author = {Christos Tryfonopoulos and Paraskevi Raftopoulou and Vinay Setty and Argiris Xiros} } @article {DBLP:journals/tdp/PoulisSLG14, title = {Apriori-based algorithms for k\(^\mboxm\)-anonymizing trajectory data}, journal = {Trans. Data Privacy}, volume = {7}, number = {2}, year = {2014}, pages = {165{\textendash}194}, url = {http://www.tdp.cat/issues11/abs.a194a14.php}, author = {Giorgos Poulis and Spiros Skiadopoulos and Grigorios Loukides and Aris Gkoulalas-Divanis} } @article {582, title = {Distributed Large-Scale Information Filtering}, journal = {Transactions on Large-Scale Data- and Knowledge-Centered Systems (TLDKS)}, volume = {13}, year = {2014}, pages = {91{\textendash}122}, abstract = {We study the problem of distributed resource sharing in peer-to-peer networks and focus on the problem of information filter- ing. In our setting, subscriptions and publications are specified using an expressive attribute-value representation that supports both the Boolean and Vector Space models. We use an extension of the distributed hash table Chord to organise the nodes and store user subscriptions, and utilise efficient publication protocols that keep the network traffic and latency low at filtering time. To verify our approach, we evaluate the proposed protocols experimentally using thousands of nodes, millions of user subscriptions, and two different real-life corpora. We also study three important facets of the load-balancing problem in such a scenario and present a novel algorithm that manages to distribute the load evenly among the nodes. Our results show that the designed protocols are scalable and efficient: they achieve expressive information filtering functionality with low message traffic and latency.}, keywords = {distributed hash tables, Information management, publish/subscribe}, author = {Christos Tryfonopoulos and Stratos Idreos and Manolis Koubarakis and Paraskevi Raftopoulou} } @article {DBLP:journals/pvldb/ElseidyASK14, title = {GRAMI: Frequent Subgraph and Pattern Mining in a Single Large Graph}, journal = {PVLDB}, volume = {7}, number = {7}, year = {2014}, pages = {517{\textendash}528}, doi = {10.14778/2732286.2732289}, url = {http://www.vldb.org/pvldb/vol7/p517-elseidy.pdf}, author = {Mohammed Elseidy and Ehab Abdelhamid and Spiros Skiadopoulos and Panos Kalnis} } @conference {553, title = {Mindmap-Inspired Semantic Personal Information Management}, booktitle = {Proceedings of the 17th International Conference on Extending Database Technology (EDBT)}, year = {2014}, month = {March}, address = {Athens, Greece}, author = {Jenny Rompa and Christos Tryfonopoulos and Costas Vassilakis and Giorgos Lepouras} } @conference {Rompa2014, title = {Mindmap-Inspired Semantic Personal Information Management}, booktitle = {Demo at the 17th International Conference on Extending Database Technology, 2014, Athens, Greece}, year = {2014}, month = {3/2014}, abstract = {Users nowadays need to manage large amounts of information, including documents, e-mails, contacts, and multimedia content. To facilitate the tasks of organisation, maintenance, and retrieval of personal information, a number of semantics-based methods have emerged; these methods employ (personal) ontologies as an underlying infrastructure for organising and querying the personal information space. In this paper we present OntoFM, a novel personal information management tool that offers a mindmap-inspired interface to facilitate user interactions with the information base. Besides serving as an information retrieval aid, OntoFM allows the user to specify and update the semantic links between information items, constituting thus a complete personal information management tool.}, doi = {10.5441/002/edbt.2014.55}, url = {http://dx.doi.org/10.5441/002/edbt.2014.55}, author = {Rompa, J. and Christos Tryfonopoulos and Costas Vassilakis and Giorgos Lepouras} } @proceedings {DBLP:conf/edbt/2014, title = {Proceedings of the 17th International Conference on Extending Database Technology, EDBT 2014, Athens, Greece, March 24-28, 2014}, year = {2014}, publisher = {OpenProceedings.org}, url = {http://openproceedings.org/html/pages/2014_edbt.html}, editor = {Sihem Amer-Yahia and Vassilis Christophides and Anastasios Kementsietsidis and Minos N. Garofalakis and Stratos Idreos and Vincent Leroy} } @conference {DBLP:conf/edbt/PoulisGLST14, title = {SECRETA: A System for Evaluating and Comparing RElational and Transaction Anonymization algorithms}, booktitle = {Proceedings of the 17th International Conference on Extending Database Technology, EDBT 2014, Athens, Greece}, year = {2014}, month = {March 24-28}, pages = {620{\textendash}623}, doi = {10.5441/002/edbt.2014.58}, url = {https://doi.org/10.5441/002/edbt.2014.58}, author = {Giorgos Poulis and Aris Gkoulalas-Divanis and Grigorios Loukides and Spiros Skiadopoulos and Christos Tryfonopoulos} } @conference {lep14a, title = {Towards a Learning Analytics Platform for Supporting the Educational Process}, booktitle = {Proceedings of the 5th Conference on Information, Intelligence, Systems \& Application (IISA2014)}, year = {2014}, month = {7}, abstract = {In this paper, we present the vision of an open source learning analytics platform, able to harvest data from different sources, including e-learning platforms and environments, registrar{\textquoteright}s information systems, alumni systems, etc., so as to provide all stakeholders with the necessary functionality to make decisions on the learning process. The platform{\textquoteright}s architecture is modular, allowing the introduction of new functionality or connection to new systems to collect needed data. All data can be analyzed and presented though interactive visualizations to find correlations between metrics, to make predictions for students or student groups, to identify best practices for instructors and let them explore {\textquoteright}what-if{\textquoteright} scenarios, to offer students personalized recommendations and personalized detailed feedback, etc. Our objective is to inform and empower all stakeholders to improve the learning experience.}, doi = {10.1109/IISA.2014.6878750}, url = {http://ieeexplore.ieee.org/document/6878750/}, author = {Giorgos Lepouras and Akrivi Katifori and Costas Vassilakis and Angela Antoniou and Nikos Platis} } @conference {Katif2014a, title = {Visualization method effectiveness in ontology-based information retrieval tasks involving entity evolution}, booktitle = {Proceedings of SMAP 2014}, year = {2014}, month = {11}, abstract = {Incorporating digital tools in the business and scientific research workflows is at the moment an on-going process, challenging and demanding as every domain has its own needs in terms of data models and information retrieval methods. The information in some domains involves entity evolution, a characteristic that introduces additional tasks, such as finding all evolution stages of an entity, and poses additional requirements for the information retrieval process. In this paper we present a user study aiming to investigate the effectiveness of current ontology browsing and visualization methods for supporting users in tasks involving research on entity evolution.}, doi = {10.1109/SMAP.2014.24}, author = {Akrivi Katifori and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @proceedings {DBLP:conf/bibe/2013, title = {13th IEEE International Conference on BioInformatics and BioEngineering, BIBE 2013, Chania, Greece, November 10-13, 2013}, year = {2013}, publisher = {IEEE Computer Society}, isbn = {978-1-4799-3163-7}, url = {http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6689795} } @proceedings {DBLP:conf/icdm/2013w, title = {13th IEEE International Conference on Data Mining Workshops, ICDM Workshops, TX, USA, December 7-10, 2013}, year = {2013}, publisher = {IEEE Computer Society}, isbn = {978-0-7695-5109-8}, url = {http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6732242}, editor = {Wei Ding and Takashi Washio and Hui Xiong and George Karypis and Bhavani M. Thuraisingham and Diane J. Cook and Xindong Wu} } @proceedings {DBLP:conf/mdm/2013-2, title = {2013 IEEE 14th International Conference on Mobile Data Management, Milan, Italy, June 3-6, 2013 - Volume 2}, year = {2013}, publisher = {IEEE Computer Society}, url = {http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?isnumber=6569035} } @conference {Margaris2013RCIS, title = {Adapting WS-BPEL scenario execution using collaborative filtering techniques}, booktitle = {IEEE 7th International Conference on Research Challenges in Information Science (RCIS)}, year = {2013}, month = {may}, publisher = {IEEE}, organization = {IEEE}, abstract = {WS-BPEL has been adopted as the predominant method for composing individual web services into higher-level business processes. The designers of WS-BPEL scenarios define at development time the specific web services that will be invoked in the context of the business process they model; in the context however of the current web, where each functionality is offered by multiple service providers, under different quality of service parameters, using a fixed BPEL scenario has been recognized to be inadequate for servicing the diverse needs of business processes clients. To this end, WS-BPEL scenario execution adaptation has been proposed, mainly allowing clients to specify quality of service policies, which drive the dynamic selection of the services that will be invoked. In this paper, we present a framework extending the quality of service-based adaptation mechanisms with collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, in the context of the same business processes.}, doi = {10.1109/rcis.2013.6577691}, author = {Dionisis Margaris and P. Georgiadis and Costas Vassilakis} } @conference {DBLP:conf/pkdd/PoulisLGS13, title = {Anonymizing Data with Relational and Transaction Attributes}, booktitle = {Machine Learning and Knowledge Discovery in Databases - European Conference, ECML PKDD 2013, Prague, Czech Republic, September 23-27, 2013, Proceedings, Part III}, year = {2013}, pages = {353{\textendash}369}, doi = {10.1007/978-3-642-40994-3_23}, url = {https://doi.org/10.1007/978-3-642-40994-3_23}, author = {Giorgos Poulis and Grigorios Loukides and Aris Gkoulalas-Divanis and Spiros Skiadopoulos} } @conference {DBLP:conf/bibe/TsafaraTS13, title = {CloudStudy: A cloud-based system for supporting multi-centre studies}, booktitle = {13th IEEE International Conference on BioInformatics and BioEngineering, BIBE 2013, Chania, Greece, November 10-13, 2013}, year = {2013}, pages = {1{\textendash}4}, doi = {10.1109/BIBE.2013.6701549}, url = {https://doi.org/10.1109/BIBE.2013.6701549}, author = {Amalia Tsafara and Christos Tryfonopoulos and Spiros Skiadopoulos} } @conference {DBLP:conf/mdm/PoulisSLG13, title = {Distance-Based k\^m-Anonymization of Trajectory Data}, booktitle = {2013 IEEE 14th International Conference on Mobile Data Management, Milan, Italy, June 3-6, 2013 - Volume 2}, year = {2013}, pages = {57{\textendash}62}, doi = {10.1109/MDM.2013.66}, url = {https://doi.org/10.1109/MDM.2013.66}, author = {Giorgos Poulis and Spiros Skiadopoulos and Grigorios Loukides and Aris Gkoulalas-Divanis} } @conference {550, title = {DS4: A Distributed Social and Semantic Search System}, booktitle = {Proceedings of 35th European Conference on Information Retrieval (ECIR)}, year = {2013}, month = {March}, address = {Moscow, Russia}, author = {Dionisis Kontominas and Paraskevi Raftopoulou and Christos Tryfonopoulos and E.G.M. Petrakis} } @conference {539, title = {DS4: Introducing Semantic Friendship in Distributed Social Networks.}, booktitle = {Proceedings of the 21st International Conference on Cooperative Information Systems (CoopIS)}, year = {2013}, month = {September}, address = {Graz, Austria}, author = {Paraskevi Raftopoulou and Christos Tryfonopoulos and E.G.M. Petrakis and Nikos Zevlis} } @article {DBLP:journals/corr/ZervakisTPKS13, title = {Full-text Support for Publish/Subscribe Ontology Systems}, journal = {CoRR}, volume = {abs/1307.2015}, year = {2013}, url = {http://arxiv.org/abs/1307.2015}, author = {Lefteris Zervakis and Christos Tryfonopoulos and Antonios Papadakis-Pesaresi and Manolis Koubarakis and Spiros Skiadopoulos} } @conference {masie2013, title = {Improving museum visitors{\textquoteright} Quality of Experience through intelligent recommendations: A visiting style-based approach}, booktitle = {Proceedings of MASIE 2013 Workshop, co-located with the 9th International Conference on Intelligent Environments IE{\textquoteright}13}, year = {2013}, month = {7}, address = {Athens, GR}, abstract = {This paper investigates the effect that smart routing and recommendations can have on improving the Quality of Experience of museum visitors. The novelty of our approach consists of taking into account not only user interests but also their visiting styles, as well as modeling the museum not as a sterile space but as a location where crowds meet and interact, impacting each visitor?s Quality of Experience. The investigation is done by an empirical study on data gathered by a custom-made simulator tailored for the museum user routing problem. Results are promising and future potential and directions are discussed.}, doi = {10.3233/978-1-61499-286-8-507}, author = {Ioanna Lykourentzou and Claude, X. and Y. Naudet and Tobias, E. and Angela Antoniou and Giorgos Lepouras and Costas Vassilakis} } @conference {Margaris2013SAC, title = {An integrated framework for QoS-based adaptation and exception resolution in WS-BPEL scenarios}, booktitle = {Proceedings of the 28th Annual ACM Symposium on Applied Computing - SAC \textquotesingle13}, year = {2013}, month = {3}, publisher = {ACM Press}, organization = {ACM Press}, abstract = {In this paper, we present a framework which incorporates runtime quality of service-based adaptation for BPEL scenarios, allowing for tailoring their execution to the diverse needs of individual users. The proposed framework also caters for automatically resolving system-level exceptions, such as machine outages or network partitionings, while both scenario execution adaptation and exception resolution maintain the transactional semantics that invocations to multiple services offered by the same provider may bear.}, doi = {10.1145/2480362.2480714}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @proceedings {DBLP:conf/pkdd/2013-3, title = {Machine Learning and Knowledge Discovery in Databases - European Conference, ECML PKDD 2013, Prague, Czech Republic, September 23-27, 2013, Proceedings, Part III}, volume = {8190}, year = {2013}, publisher = {Springer}, isbn = {978-3-642-40993-6}, doi = {10.1007/978-3-642-40994-3}, url = {https://doi.org/10.1007/978-3-642-40994-3}, editor = {Hendrik Blockeel and Kristian Kersting and Siegfried Nijssen and Filip Zelezn{\'y}} } @article {antoniou13x, title = {A methodology for the design of online exhibitions}, journal = {DESIDOC Journal of Library and Information Technology}, volume = {33}, number = {3}, year = {2013}, pages = {158{\textendash}167}, abstract = {The process of designing systems or products largely depends on a number of decisions, like {\textquotedblleft}who do I design for?{\textquotedblright}, {\textquotedblleft}what should my product do?{\textquotedblright}, {\textquotedblleft}what are the user requirements?{\textquotedblright} etc. The developing teams usually base their decisions on experience and/or heuristics and this is particularly the case, in the development of online products and especially online exhibitions. The different solutions are frequently case studies of specific museums or institutions that wish to provide online content to actual or possible visitors. In addition, the interdisciplinary nature of the endeavor, involving museology, technology but also education, poses important design problems. In the following sections, we present a generic methodology for the design of online exhibitions, using top-down processes and transferable findings across museum types that wish to assist the designers during the early decision stages. This paper provides an introduction to the field, emphasising its interdisciplinary nature and reviews related work in the area of online exhibition design. It also presents an overview of the methodology, elaborating on the individual methodology steps; in particular, the processes for determining the visitors{\textquoteright} perception of the museum (degree of museumness); the museum needs that require to be supported; the educational approach to be adopted; the relevance to life-long learning activities; the approach to adaptivity; and user involvement have been reviewed.}, author = {Angela Antoniou and Giorgos Lepouras and Costas Vassilakis} } @article {vassiliadis2011d, title = {Modelling and performance study of finite-buffered blocking multistage interconnection networks supporting natively 2-class priority routing traffic}, journal = {Journal of Network and Computer Applications}, volume = {36(2)}, number = {2}, year = {2013}, month = {mar}, pages = {723{\textendash}737}, publisher = {Elsevier BV}, abstract = {Contemporary networks accommodate handling of multiple priorities, aiming to provide suitable QoS levels to different traffic classes. In the presence of multiple priorities, a scheduling algorithm is employed to select each time the next packet to transmit over the data link. Class-based Weighted Fair Queuing (CBWFQ) scheduling and its variations, is widely used as a scheduling technique, since it is easy to implement and prevents the low-priority queues from being completely neglected during periods of high-priority traffic. By using this scheduling, low-priority queues have the opportunity to transmit packets even though the high-priority queues are not empty. In this paper, the modeling, analysis and performance evaluation of a single-buffered, dual priority multistage interconnection network (MIN) operating under the CBWFQ scheduling policy is presented. Performance evaluation is conducted through simulation, and the performance measures obtained can be valuable assets for MIN designers, in order to minimize the overall deployment costs and delivering efficient systems.}, doi = {10.1016/j.jnca.2012.12.016}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @article {Vasiliadis-2013x, title = {Performance Tuning of Dual-priority Delta Networks through Queuing Scheduling Disciplines}, journal = {Journal of Communications Software and Systems}, volume = {9(4)}, number = {4}, year = {2013}, month = {12/2013}, pages = {222-235}, publisher = {Croatian Communications and Information Society}, abstract = {Differentiated Services (DiffServ) and other scheduling strategies are now widespread in the traditional, {\textquotedblleft}best effort{\textquotedblright} Internet. These Internet Architectures offer Quality of Service (QoS) guarantees for important customers at the same time as supporting less critical applications of lower priority. Strict priority queuing (PQ), weighted round robin (WRR), and class-based weighted fair queuing (CBWFQ) are three common scheduling disciplines for differentiation of services in telecommunication networks. In this paper, a comparative performance study of the above PQ, WRR and CBWFQ queuing scheduling policies applied on a double-buffered, 6-stage Multistage Interconnection Network (MIN) that natively supports a 2-class priority mechanism is presented and analyzed using simulation experiments. We also consider a 10-stage MIN, to validate that the conclusions drawn from the 6-stage MIN apply to MINs of different sizes. The findings of this paper can be used by MIN designers to optimally configure their networks.}, doi = {10.24138/jcomss.v9i4.143}, url = {https://hrcak.srce.hr/180111}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @conference {DBLP:conf/icdm/PoulisSLG13, title = {Select-Organize-Anonymize: A Framework for Trajectory Data Anonymization}, booktitle = {13th IEEE International Conference on Data Mining Workshops, ICDM Workshops, TX, USA, December 7-10, 2013}, year = {2013}, pages = {867{\textendash}874}, doi = {10.1109/ICDMW.2013.136}, url = {https://doi.org/10.1109/ICDMW.2013.136}, author = {Giorgos Poulis and Spiros Skiadopoulos and Grigorios Loukides and Aris Gkoulalas-Divanis} } @conference {gala2013, title = {User Profiling: Towards a Facebook Game that Reveals Cognitive Style}, booktitle = {Proceedings of the GALA 2013 conference}, year = {2013}, month = {10}, pages = {349{\textendash}353}, address = {Paris, FR}, abstract = {This paper presents an innovative approach based on social-network gaming, which will extract players? cognitive styles for personalization purposes. Cognitive styles describe the way individuals think, perceive and remember information and can be exploited to personalize user interaction. Questionnaires are usually employed to identify cognitive styles, a tedious process for most users. Our approach relies on a Facebook game for discovering potential visitors? cognitive styles with an ultimate goal of enhancing the overall visitors{\textquoteright} experience in the museum. By hosting such a game on the museum?s webpage and on Facebook, the museum aims to attract new visitors, as well as to support the user profiling process.}, doi = {10.1007/978-3-319-12157-4_28}, author = {Angela Antoniou and Ioanna Lykourentzou and Rompa, J. and Tobias, E. and Giorgos Lepouras and Costas Vassilakis and Y. Naudet} } @article {vassiliadis-hind2012, title = {Class-Based Weighted Fair Queuing Scheduling on Dual-Priority Delta Networks}, journal = {Journal of Network and Computer Applications}, volume = {2012}, number = {XX}, year = {2012}, pages = {13 pages}, abstract = {In this paper, we model, analyze and evaluate the performance of a 2-class priority architecture for finite-buffered Multistage Interconnection Networks (MINs). The MIN operation modelling is based on a state diagram, which includes the possible MIN states, transitions and conditions under which each transition occurs. Equations expressing state and transition probabilities are subsequently given, providing a formal model for evaluating the MIN{\textquoteright}s performance. The proposed architecture{\textquoteright}s performance is subsequently analyzed using simulations; operational parameters, including buffer length, MIN size, offered load and ratios of high priority packets which are varied across experiments to gain insight on how each parameter affects the overall MIN performance. The 2-class priority MIN performance is compared against the performance of single priority MINs, detailing the performance gains and losses for packets of different priorities. Performance is assessed by means of the two most commonly used factors, namely packet throughput and packet delay, while a performance indicator combining both individual factors is introduced, computed and discussed. The findings of this study can be used by network and interconnection system designers in order to deliver efficient systems while minimizing the overall cost. The performance evaluation model can also be applied to other network types, providing the necessary data for network designers to select optimal values for network operation parameters.}, doi = {10.1155/2012/859694}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @article {vassiliadis-jpeds2012, title = {Class-based weighted fair queuing scheduling on quad-priority Delta Networks}, journal = {International Journal of Parallel, Emergent and Distributed Systems}, volume = {27}, number = {5}, year = {2012}, month = {oct}, pages = {435{\textendash}457}, publisher = {Informa UK Limited}, abstract = {Contemporary networks support multiple priorities, aiming to differentiate the QoS levels offered to individual traffic classes. Support for multiple priorities necessitates the introduction of a scheduling algorithm, to select each time the next packet to transmit over the data link. Class-based Weighted Fair Queuing (CBWFQ) scheduling and its variations, is widely used as a scheduling technique, since it is easy to implement and prevents the low-priority queues from starvation, i.e. receiving no service during periods of high-priority traffic. CBWFQ effectively thus offers low-priority queues the opportunity to transmit packets even though the high-priority queues are not empty. In this paper, we present the modeling and performance evaluation of a single-buffered, four-priority multistage interconnection network (MIN) operating under the CBWFQ scheduling policy. Performance evaluation is conducted through simulation, and the performance metrics obtained can be used by MIN designers to set the appropriate queue weights according to the expected traffic and the desired QoS levels for each priority class, delivering efficient thus systems.}, doi = {10.1080/17445760.2012.712694}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @article {benou2012b, title = {A context management architecture for m-commerce applications}, journal = {Central European Journal of Computer Science, Versita, co-published with Springer Verlag}, volume = {2}, number = {2}, year = {2012}, pages = {87{\textendash}117}, abstract = {Mobile commerce applications operate in highly dynamic environments with diverse characteristics and interesting challenges. The characteristics and conditions of these environments {\textendash}called context{\textendash}, can be exploited to provide adaptive mobile services, in terms of user interface, functionality and content, in order to offer more effective m-commerce. Today, building adaptive mobile services is a complex and time-consuming task due to the lack of standardized methods, tools and architectures for the identification, representation and management of the context. Addressing some of these issues, recent works have provided formal extensions for various stages of the m-commerce application lifecycle, such as extended UML class diagrams for building design models and have used context parameters in order to offer adaptive applications. Using these works as the basis, in this paper we propose a context management architecture, which accommodates the requirements that have been identified for m-commerce applications. The proposed architecture is evaluated in terms of completeness, complexity, performance and utility, and compared against other approaches proposed in the literature regarding its suitability for supporting context-aware m-commerce applications.}, keywords = {adaptivity, context, context management, context-awareness, mobile commerce, software architecture}, doi = {10.2478/s13537-012-0010-z}, url = {https://link.springer.com/article/10.2478/s13537-012-0010-z}, author = {Poulcheria Benou and Costas Vassilakis} } @article {benou2012, title = {Context Management for m-Commerce Applications: Determinants, Methodology and the Role of Marketing}, journal = {Information Technology and Management, Springer-Verlag}, volume = {13(2)}, year = {2012}, pages = {91 {\textendash} 111}, abstract = {Studying consumer behaviour and usage of environmental determinants in the mobile services domain contributes to the identification of context information which is critical for the effective operation of mobile commerce applications. Exploiting this information towards providing enhanced and innovative mobile services offers a competitive advantage within the highly demanding domain of m-commerce applications. However, in order to effectively exploit such context information, there is a need to design the necessary methods, software tools and information systems that will be employed for collecting, processing and disseminating this information. In this paper we develop a theoretical framework which defines the context information necessary for m-commerce applications, taking into account relevant marketing dimensions as well as privacy protection perspectives. Then, this framework is operationalized through the design of an appropriate software architecture which enables the standardization and management of context information.}, doi = {10.1007/s10799-012-0120-2}, author = {Poulcheria Benou and Costas Vassilakis and Adam Vrechopoulos} } @article {Giannikopoulos2011, title = {A distributed recommender system architecture}, journal = {International Journal of Web Engineering and Technology}, volume = {7}, number = {3}, year = {2012}, pages = {203{\textendash}227}, abstract = {In contemporary internet architectures, including server farms and blog aggregators, web log data may be scattered among multiple cooperating peers. In order to perform content personalization through provision of recommendations on such architectures, it is necessary to employ a recommendation algorithm; however the majority of such algorithms are centralized, necessitating excessive data transfers and exhibiting performance issues when the number of users or the volume of data increase. In this paper we propose an approach where the clickstream information is distributed to a number of peers, which cooperate for discovering frequent patterns and for generating recommendations, introducing (a) architectures that allow the distribution of both the content and the clickstream database to the participating peers and (b) algorithms that allow collaborative decisions on the recommendations to the users, in the presence of scattered log information. The proposed approach may be employed in various domains, including digital libraries, social data, server farms and content distribution networks.}, doi = {10.1504/IJWET.2012.048517}, author = {Giannikopoulos, P. and Costas Vassilakis} } @article {DBLP:journals/tkde/BourosSDSS12, title = {Evaluating Path Queries over Frequently Updated Route Collections}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {24}, number = {7}, year = {2012}, pages = {1276{\textendash}1290}, doi = {10.1109/TKDE.2011.30}, url = {https://doi.org/10.1109/TKDE.2011.30}, author = {Panagiotis Bouros and Dimitris Sacharidis and Theodore Dalamagas and Spiros Skiadopoulos and Timos K. Sellis} } @conference {554, title = {Full-text Support for Publish/Subscribe Ontology Systems}, booktitle = {Proceedings of the Extended Semantic Web Conference (ESWC)}, year = {2012}, month = {May}, address = {Crete, Greece}, author = {Lefteris Zervakis and Christos Tryfonopoulos and Antonios Papadakis-Pesaresi and Manolis Koubarakis and Spiros Skiadopoulos} } @article {DBLP:journals/corr/abs-1207-0135, title = {Privacy Preservation by Disassociation}, journal = {CoRR}, volume = {abs/1207.0135}, year = {2012}, url = {http://arxiv.org/abs/1207.0135}, author = {Manolis Terrovitis and John Liagouris and Nikos Mamoulis and Spiros Skiadopoulos} } @article {DBLP:journals/pvldb/TerrovitisLMS12, title = {Privacy Preservation by Disassociation}, journal = {PVLDB}, volume = {5}, number = {10}, year = {2012}, pages = {944{\textendash}955}, doi = {10.14778/2336664.2336668}, url = {http://vldb.org/pvldb/vol5/p944_manolisterrovitis_vldb2012.pdf}, author = {Manolis Terrovitis and John Liagouris and Nikos Mamoulis and Spiros Skiadopoulos} } @mastersthesis {526, title = {A Software Development Methodology and a Software Architecture for Context-Aware M-Commerce Applications}, volume = {Ph.D. thesis}, year = {2012}, month = {02/2012}, pages = {369}, school = {University of the Peloponnese}, type = {Doctoral}, address = {Tripolis}, abstract = {

Mobile commerce is gaining importance in the recent years, as an enhanced version of e-commerce for the moving user. The mobile services through which m-commerce takes place operate in highly dynamic environments with diverse characteristics and under varying conditions. The characteristics and conditions of these environments {\textendash}called context{\textendash} can be exploited in order to offer a suitable user experience and deliver innovative and enhanced mobile services that will facilitate user interaction, attract new customers and maintain existing ones. Therefore, mobile commerce applications adhering to {\textquotedblleft}anytime and anywhere{\textquotedblright} paradigm are required to be flexible. They should be able to adapt their user-perceived constituent parts, i.e. their interface, services and content towards a certain context. Several proposals for definition of context have been already proposed originating from various areas related to mobile commerce. However, an integrated, formal and methodological approach for the determination and representation of context, adjusted to special characteristics of mobile commerce applications, has not been insofar presented. This is one challenge we address in this thesis, through a conceptual model that includes: i) a clear and formal definition of context, ii) the depiction of its specific characteristics as metadata, iii) a methodology for its determination and iv) the presentation of an extension of UML class and case diagrams for its representation, all of them tailored to the special nature of mobile commerce applications.

Once the context information for an m-commerce application has been determined, the next step in order to achieve the goal of adaptivity is to capture the context information from its sources, process and distribute it to the software components that will use it. In order to offer a complete suite of tools for context management, we propose a software architecture for context information management suitable for m-commerce applications. We describe the functionality and characteristics of its components, as well as the interaction among these different components.

The usage of context information in order to achieve the ultimate goal of adaptivity should be done from a subsystem designed in such way that will simplify and homogenize the relevant processes and at the same time promote the independence of the code of the main application from the adaptation code. Addressing this issue, in this thesis we propose an approach for developing adaptive mobile commerce applications, adhering to the separation of concerns principle, which is offered by the aspect-oriented paradigm. By clearly separating the work required for the development of the application logic from that required for enabling application{\textquoteright}s adaptive behavior, this approach reduces the development effort and at the same time promotes the flexibility, manageability and maintainability of adaptive m-commerce applications. }, keywords = {Context Information, context management, context-awareness, mobile commerce, Mobile Commerce Applications, Software Adaptation, Software Architecture for M-commerce Applications, Software Methodology for M-commerce Applications}, url = {https://soda.dit.uop.gr/sites/soda.dit.uop.gr/files//Benou_PhDThesis.pdf}, author = {Poulcheria Benou}, editor = {Costas Vassilakis} } @article {lyk11a, title = {Wikis in enterprise settings: a survey}, journal = {Enterprise Information Systems}, volume = {6}, number = {1}, year = {2012}, month = {feb}, pages = {1-53}, publisher = {Informa UK Limited}, abstract = {The wiki technology is increasingly being used in corporate environments to facilitate a broad range of tasks. This survey examines the use of wikis on a variety of organisational tasks that include the codification of explicit and tacit organisational knowledge and the formulation of corporate communities of practice, as well as more specific processes such as the collaborative information systems development, the interactions of the enterprise with third parties, management activities and organisational response in crisis situations. For each one of the aforementioned corporate functions, the study examines the findings of related research literature to highlight the advantages and concerns raised by the wiki usage and to identify specific solutions addressing them. Finally, based on the above findings, the study discusses various aspects of the wiki usage in the enterprise and identifies trends and future research directions on the field.}, doi = {10.1080/17517575.2011.580008}, url = {http://dx.doi.org/10.1080/17517575.2011.580008}, author = {Ioanna Lykourentzou and Foteini Dagka and Katerina Papadaki and Giorgos Lepouras and Costas Vassilakis} } @article {DBLP:journals/pvldb/MansourASK11, title = {ERA: Efficient Serial and Parallel Suffix Tree Construction for Very Long Strings}, journal = {PVLDB}, volume = {5}, number = {1}, year = {2011}, pages = {49{\textendash}60}, doi = {10.14778/2047485.2047490}, url = {http://www.vldb.org/pvldb/vol5/p049_essammansour_vldb2012.pdf}, author = {Essam Mansour and Amin Allam and Spiros Skiadopoulos and Panos Kalnis} } @article {DBLP:journals/corr/abs-1109-6884, title = {ERA: Efficient Serial and Parallel Suffix Tree Construction for Very Long Strings}, journal = {CoRR}, volume = {abs/1109.6884}, year = {2011}, url = {http://arxiv.org/abs/1109.6884}, author = {Essam Mansour and Amin Allam and Spiros Skiadopoulos and Panos Kalnis} } @article {vassiliadis2010c, title = {Modelling and performance evaluation of a novel internal priority routing scheme for finite-buffered multistage interconnection networks}, journal = {International Journal of Parallel, Emergent and Distributed Systems}, volume = {26(5)}, year = {2011}, pages = {381{\textendash}397}, abstract = {In this paper, the modelling, analysis and performance evaluation of a novel architecture for internal priority finite-buffered Multistage Interconnection Networks (MINs) is presented. We model the proposed architecture giving the details of its operation and describing its states and detailing conditions and effects of state transition; we also provide a formal model for evaluating its performance. The proposed architecture{\textquoteright}s performance is subsequently analyzed under the uniform traffic condition, considering various offered loads, buffer-lengths and MIN sizes, using simulations. We compare the internal priority scheme vs. the non priority (or single priority) scheme, by gathering metrics for the two most important network performance factors, namely packet throughput and the mean time a packet needs to traverse the network. We demonstrate and quantify the improvements on MIN performance stemming from the introduction of priorities in terms of throughput and a combined performance indicator which depicts the overall performance of the MIN. These performance measures can be valuable assets for designers of parallel multiprocessor systems and networks in order to minimize the overall deployment costs and delivering efficient systems.}, doi = {10.1080/17445760.2010.539218}, url = {https://www.tandfonline.com/doi/abs/10.1080/17445760.2010.539218}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis and E. Glavas} } @conference {Rompa2011, title = {OntoFM: A Personal Ontology-based File Manager for the Desktop}, booktitle = {Demo at the 10th International Web Conference, 2011, Bonn, Germany}, year = {2011}, month = {10}, abstract = {OntoFM is a novel file manager that bases its interactivity on the user?s personal ontology, offering semantic browsing and searching mechanisms for locating files, a mind map inspired ontology visualization, and simple-to-use intuitive functionality that encourages less experienced users. The implementation of OntoFM is based on Protege, an extensible open source ontology editor and knowledge-base framework. The file manager is implemented as a Protege tab widget, retrieving information from your personal ontology. Ontology visualization is based upon the OntoGraf plug-in which has been extended to comply with the mind map paradigm. Currently the ontology visualization pane permits only navigational functions, while other ontology management functions have been hidden to ease the complexity of the user interface.}, url = {https://arxiv.org/abs/1307.2018}, author = {Rompa, J. and Giorgos Lepouras and Costas Vassilakis and Christos Tryfonopoulos} } @conference {560, title = {OntoFM: A Personal Ontology-based File Manager for the Desktop}, booktitle = {Proccedings of the International Semantic Web Conference (ISWC)}, year = {2011}, month = {October}, address = {Bonn, Germany}, author = {Jenny Rompa and Giorgos Lepouras and Costas Vassilakis and Christos Tryfonopoulos} } @article {vasiliadis2011a, title = {Performance Analysis of Dual-Priority Multilayer Multistage Interconnection Networks under Multicast Environment}, journal = {Journal of Networks}, volume = {June}, year = {2011}, pages = {858{\textendash}871}, abstract = {Next-generation network architectures strive to achieve high bandwidth and ultralow latency for the packets traversing the offered end-to-end paths. Multistage Interconnection Networks (MINs) are often employed for implementing NGNs, but while MINs are fairly flexible in handling varieties of traffic loads, they tend to quickly saturate under broadcast and multicast traffic, especially at increasing size networks. As a response to this issue, multilayer MINs have been proposed, however their performance prediction and evaluation has not been studied sufficiently insofar. In this paper, we evaluate and discuss the performance of multilayer MINs under multicast traffic, considering also two levels of packet priorities, since support for multiple QoS levels is an indispensible requirement for NGNs. Different offered loads and buffer size configurations are examined in this context, and performance results are given for the two most important network performance factors, namely packet throughput and delay. We also introduce and calculate a universal performance fac{\textlnot}tor, which includes the importance aspect of each of the above main performance factors. The findings of this study can be used by NGN system designers in order to predict the performance of each configuration and adjust the design of their communication infrastructure to the traffic requirements at hand.}, keywords = {banyan networks, multicast traffic, multilayer networks, Multistage interconnection networks, performance analysis}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @article {vasiliadis11, title = {Performance Analysis of Multi-Layered Multi-Priority Asymetric-Sized Delta Networks}, journal = {Journal of Computer Systems, Networks, and Communications}, volume = {to appear}, year = {2011}, pages = {12}, abstract = {In this paper the performance of multi-layered asymmetric-sized finite-buffered Delta Networks supporting multi-class routing traffic is presented and analyzed in the uniform traffic conditions under various loads using simulations. The rationale behind introducing asymmetric-sized buffered systems is to have a better exploitation of available buffer spaces, while the implementation of multi-layered architecture is applied in order to further improve the overall performance of network. The findings of this performance evaluation can be used by network designers for drawing optimal configurations while setting up the network, so as to best meet the performance and cost requirements under the anticipated traffic load and quality of service specifications.}, doi = {10.1155/2011/723102}, url = {https://www.hindawi.com/journals/jcnc/2011/723102/}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @conference {538, title = {Pricing Information Goods in Distributed Agent-based Information Filtering}, booktitle = {Proceedings of the 19th International Conference on Cooperative Information Systems (CoopIS)}, year = {2011}, month = {October}, address = {Crete, Greece}, author = {Christos Tryfonopoulos and Laura Maria Andreescu} } @conference {benou2011a, title = {A Software Architecture for Provision of Context-Aware Web-based m-Commerce Applications}, booktitle = {Proceedings of the 11th IEEE International Conference on Computer and Information Technology (CIT 2011)}, year = {2011}, month = {8}, publisher = {IEEE Computer Society}, organization = {IEEE Computer Society}, abstract = {Mobile commerce is gaining significant importance in the recent years as an alternative option of e-commerce for the moving user. The mobile applications through which mcommerce takes place operate in highly dynamic environments with diverse characteristics and under varying conditions. The characteristics and conditions of these environments {\textendash}called context{\textendash} should be exploited in order to provide adaptive services; services that offer a suitable user experience and deliver innovative and enhanced capabilities that will facilitate user interaction, attract new customers and maintain existing ones. The goal of adaptivity is realized through the adaptation of user interface, functionality and content of applications using the context information. Therefore, context-awareness constitutes an essential aspect {\textendash} almost a requirement {\textendash} of mobile services. In order to realize context-aware services, there is a necessity to capture the context information from its sources, process and distribute it to the software components that will use it. In this paper, we propose a software architecture for context information management suitable for m-commerce applications. We describe the functionality and characteristics of its components, as well as the interaction among these different components}, doi = {10.1109/CIT.2011.20}, author = {Poulcheria Benou and Costas Vassilakis} } @conference {Akim2011a, title = {Spreading Activation for Web Scale Reasoning: Promise and Problems}, booktitle = {WebSci 11, poster presentation}, year = {2011}, month = {6}, pages = {1-4}, abstract = {Various forms of spreading activation has been used in a number of web systems, not least in the PageRank algorithm. In our own work we have been using this as a technique for managing context over small and large ontologies, and both our own work and that in LarKC suggests that spreading activation has the potential to aid in reasoning over web-scale data sets including the growing set of linked open data resources. Of particular importance is that spreading activation can be applied locally to a dynamic selfselecting working set of an (practically) unbound linked data collection, as well as globally to the entire collection. However, this potential does not come without problems, some concerning the nature of the algorithm on any large data set, and some more to do with the particular nature of linked open data.}, author = {Nazihah Md. Akim and Alan Dix and Akrivi Katifori and Giorgos Lepouras and Nadeem Shabir and Costas Vassilakis} } @conference {wallace11a, title = {Supporting User Roles in Ontology Fuzzification}, booktitle = {Proceedings of the 6th International Workshop on Semantic media adaptation and personalization (SMAP)}, year = {2011}, month = {dec}, publisher = {IEEE Computer Society}, organization = {IEEE Computer Society}, abstract = {Manual ontology development is clearly a strenuous task. Whilst a variety of ontological engineering methodologies exist, their actual application is far from trivial, mainly due to the widely diverse nature of the tasks involved. In this work we study these tasks and identify the different types of human experts that are best suited to perform each one. As a result, we present a cooperative version of an ontological engineering methodology, together with a graphical tool that supports it.}, keywords = {domain expert, fuzzification, knowledge engineer, ontology development, user roles}, doi = {10.1109/smap.2011.24}, url = {https://www.computer.org/csdl/proceedings/smap/2011/4524/00/4524a057.pdf}, author = {Manolis Wallace and Panos Alexopoulos and Ioannis Papafragkos and Costas Vassilakis} } @article {antoniou11, title = {Towards a methodological framework for the cognitive-behavioural evaluation of educational e-games}, journal = {International Journal of Learning Technology}, volume = {6}, number = {3}, year = {2011}, pages = {263{\textendash}287}, abstract = {The proposed methodological framework reviews and uses knowledge from the field of cognitive psychology in order to evaluate aspects of educational games. In particular, we concentrate on two components of human cognition that play a central role to learning, namely memory and motivation. After having reviewed theories in the field, we created a questionnaire in order to evaluate educational games. The questionnaire incorporates different experimental findings of cognitive psychology. Especially, we have applied Maslow{\textquoteright}s motivation theory, Behavioural findings on reinforcement, experimental findings about attention and memory. We present the results obtained from the evaluation of two games, PAC-MAN and Mega Jump. The results confirmed the user ratings of the two games, showing that there seem to be cognitive reasons for the success/failure of different games. Finally, lists of guidelines for developers and instructors are included.}, doi = {10.1504/11.43580}, author = {Angela Antoniou and Dimitris Diakakis and Giorgos Lepouras and Costas Vassilakis} } @article {benou2010, title = {The Conceptual Model of Context for Mobile Commerce Applications}, journal = {Electronic Commerce Research, Springer-Verlag}, volume = {10(2)}, year = {2010}, pages = {139-165}, abstract = {Mobile commerce applications adhering to anytime and anywhere paradigm, required to be flexible. They should be able to adapt their interface, services and content towards a certain context. Several proposals for definition of context have been already proposed originating from various areas related to mobile commerce. However, an integrated, formal and methodological approach for the determination and representation of context, adjusted to special characteristics of mobile commerce applications, has not been insofar presented. This is the challenge we address in this paper, through a conceptual model that includes: i) a clear and formal definition of context, ii) the depiction of its specific characteristics as metadata, iii) a methodology for its determination and iv) the presentation of an extension of class diagrams of UML for its representation, all of them tailored to the special nature of mobile commerce applications.}, doi = {10.1007/s10660-010-9050-4}, author = {Poulcheria Benou and Costas Vassilakis} } @article {dix2010b, title = {From the web of data to a world of action}, journal = {Journal of Web Semantics}, volume = {8 issue 4}, year = {2010}, pages = {394-408}, abstract = {This paper takes as its premise that the web is a place of action, not just information, and that the purpose of global data is to serve human needs. The paper presents several component technologies, which together work towards a vision where many small micro-applications can be threaded together using automated assistance to enable a unified and rich interaction. These technologies include data detector technology to enable any text to become a start point of semantic interaction; annotations for web-based services so that they can link data to potential actions; spreading activation over personal ontologies, to allow modelling of context; algorithms for automatically inferring {\textquoteleft}typing{\textquoteright} of web-form input data based on previous user inputs; and early work on inferring task structures from action traces. Some of these have already been integrated within an experimental web-based (extended) bookmarking tool, Snip!t, and a prototype desktop application On Time, and the paper discusses how the components could be more fully, yet more openly, linked in terms of both architecture and interaction. As well as contributing to the goal of an action and activity-focused web, the work also exposes a number of broader issues, theoretical, practical, social and economic, for the Semantic Web.}, doi = {10.1016/j.websem.2010.04.007}, author = {Alan Dix and Giorgos Lepouras and Akrivi Katifori and Costas Vassilakis and Tiziana Catarci and Antonella Poggi and Yannis Ioannidis and Miguel Morae and I. Daradimos and Nazihah Md.Akima and Shah Rukh Humayound and Fabio Terella} } @article {torou2010, title = {Historical research in archives: user methodology and supporting tools}, journal = {International Journal on Digital Libraries}, volume = {11(1)}, year = {2010}, pages = {25{\textendash}36}, abstract = {Historic research involves finding, using, and correlating informationwithin primary and secondary sources, in order to communicate an understanding of past events. In this process, historians employ their scientific knowledge, experience, and intuition to formulate queries (who was involved in an event, when did an event occur etc.), and subsequently try to locate the pertinent information from their sources. In this article, the authors investigate how historians formulate queries, which query terms are chosen, and how historians proceed in searching for related information in sources. The insight gained from this investigation can be subsequently used for organizing documentswithin historical source repositories and building tools that will enable historians to access the needed informationmore rapidly and fully.}, doi = {10.1007/s00799-010-0062-4}, author = {Elena Torou and Akrivi Katifori and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @article {vasiliadis2010a, title = {Improving performance of a wireless multimedia traffic-oriented network through prediction of routing}, journal = {International Journal on Information Technologies \& Security}, volume = {3}, year = {2010}, pages = {3-16}, abstract = {Wireless Local Area Networks (WLANs) have developed into a viable technology to support multimedia traffic and are expected to support multimedia services with guaranteed Quality of Service (QoS) for diverse traffic types (video, audio, and data). In this paper, we consider the incorporation of prediction into a generic distance-vector routing protocol for WLANs, evaluate the performance of the resulting routing scheme. Our study considers the enhancement of Distributed Bellman-Ford algorithm, which is a widely used algorithm, and assesses the effectiveness of the enhanced version on top of a fourth generation system (4-G). In order to compare the performance of the standard protocol against that of the prediction-enhanced version, we gather metrics for the two most important network performance factors, namely packet throughput and delay under different mobility and traffic conditions, using the simulation environment of NS-2. Both medium- and high-mobility configurations have been considered in this study.}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @article {Katifori10a, title = {Ontologies and the brain: Using spreading activation through ontologies to support personal interaction}, journal = {Cognitive Systems Research}, volume = {Volume 11, Issue 1}, year = {2010}, note = {cited By (since 1996) 0; Article in Press}, pages = {25-41}, abstract = {Ontologies, as knowledge engineering tools, allow information to be modelled in ways resembling to those used by the human brain, and may be very useful in the context of personal information management (PIM) and task information management (TIM). This work proposes the use of ontologies as a long-term knowledge store for PIM-related information, and the use of spreading activation over ontologies in order to provide context inference to tools that support TIM. Details on the ontology creation and content are provided, along with a full description of the spreading activation algorithm and its preliminary evaluation. Β{\textcopyright} 2009 Elsevier B.V.}, doi = {10.1016/j.cogsys.2009.02.001}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-62249112875\&partnerID=40\&md5=7d25fb986738b4c71a627b3fec24c58d}, author = {Akrivi Katifori and Costas Vassilakis and Alan Dix} } @conference {594, title = {Peer Rewiring in Semantic Overlay Networks under Churn}, booktitle = {Proceedings of the 18th International Conference on Cooperative Information Systems (CoopIS)}, year = {2010}, month = {October}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {Crete, Greece}, abstract = {Semantic overlay networks have been proposed as a way to organise peer-to-peer networks; peers that are semantically, thematically or socially similar are discovered and logically organised into groups. Efficient content retrieval is then performed by routing the query towards peer groups based on their likelihood to match the query. In this paper, we study the behaviour of semantic overlay networks that support full- fledged information retrieval in the presence of peer churn. We adopt a model for peer churn, and study the effect of network dynamics on peer organisation and retrieval performance. The overlay network is evaluated on a realistic peer-to-peer environment using real-world data and queries, and taking into account the dynamics of user-driven peer participation. Using this evaluation, we draw conclusions on the performance of the system in terms of clustering efficiency, communication load and retrieval accuracy in such a realistic setting.}, author = {Paraskevi Raftopoulou and E.G.M. Petrakis} } @article {vasiliadis2011b, title = {Performance Study of Multi-Layered Multistage Interconnection Networks under Hotspot Traffic Conditions}, journal = {Journal of Computer Systems, Networks, and Communications}, volume = {2010}, year = {2010}, pages = {11 pages}, abstract = {The performance of Multistage Interconnection Networks (MINs) under hotspot traffic, where some percentage of the traffic is targeted at single nodes, which are also called hot-spots, is of crucial interest. The prioritizing of packets has already been proposed at previous works as alleviation to the tree saturation problem, leading to a scheme that natively supports 2-class priority traffic. In order to prevent hotspot traffic from degrading uniform traffic we expand previous studies by introducing multi-layer Switching Elements (SEs) at last stages in an attempt to balance between MIN performance and cost. In this paper the performance evaluation of dual-priority, double-buffered, multi-layer MINs under single hotspot setups is presented and analyzed using simulation experiments. The findings of this paper can be used by MIN designers to optimally configure their networks}, keywords = {Hotspot traffic, multi-layer networks, Multistage interconnection networks, Performance evaluation}, doi = {10.1155/2010/403056}, url = {https://www.hindawi.com/journals/jcnc/2010/403056/}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @article {DBLP:journals/tkde/ClementiniSBT10, title = {A Reasoning System of Ternary Projective Relations}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {22}, number = {2}, year = {2010}, pages = {161{\textendash}178}, doi = {10.1109/TKDE.2009.79}, url = {https://doi.org/10.1109/TKDE.2009.79}, author = {Eliseo Clementini and Spiros Skiadopoulos and Roland Billen and Francesco Tarquini} } @article {dix2010, title = {Spreading Activation Over Ontologies: From Personal Context To Web Scale Reasoning}, journal = {International Journal of Semantic Computing}, volume = {Special issue on Web Scale Reasoning}, year = {2010}, pages = {59{\textendash}102}, abstract = {This paper describes methods to allow spreading activation to be used on web-scale information resources. Existing work has shown that spreading activation can be used to model context over small personal ontologies, which can be used to assist in various user activities, for example, in autocompleting web forms. This previous work is extended and methods are developed by which large external repositories, including corporate information and the web, can be linked to the user?s personal ontology and thus allow automated assistance that is able to draw on the entire web of data. The basic idea is augment the personal ontology with cached data from external repositories, where the choice of what data to fetch or discard is related to the level of activation of entities already in the personal ontology or cached data. This relies on the assumption that the working set of highly active entities is relatively small; empirical results are presented, which suggest these assumptions are likely to hold. Implications of the techniques are discussed for user interaction and for the social web. In addition, warm world reasoning is proposed, applying rule-based reasoning over activate entities, potentially merging symbolic and sub-symbolic reasoning over web-scale knowledge bases.}, doi = {10.1142/S1793351X10000973}, author = {Alan Dix and Akrivi Katifori and Giorgos Lepouras and Costas Vassilakis and Nadeem Shabir} } @conference {537, title = {Anonymity and Censorship Resistance in Unstructured Overlay Networks}, booktitle = {Proceedings of the 17th International Conference on Cooperative Information Systems (CoopIS)}, year = {2009}, month = {November}, address = {Vilamoura, Portugal}, author = {Michael Backes and Marek Hamerlik and Alessandro Linari and Matteo Maffei and Christos Tryfonopoulos and Gerhard Weikum} } @conference {torou2009a, title = {Capturing the historical research methodology: an experimental approach}, booktitle = {Proceedings of International Conference of Education, Research and Innovation (ICERI 2009)}, year = {2009}, month = {11}, abstract = {This paper presents the results of a study on how historians conduct research in a historical archive, and the methodologies they use while searching. Historic research involves finding, using, interpreting and correlating information within primary and secondary sources, in order to understand past events. The collection of historical data is accomplished through methodical and comprehensive research in primary and secondary sources. An important factor in our study was to understand what kind of data and/or information historians are looking for in a library/historical archive, either printed or digitized, and which research methodologies or research models they use while they investigate a historical archive. Since this issue has not been addressed insofar, and therefore there are no methods for elucidating research methodologies or research models that historians employ / use, we formulated a questionnaire comprising of seven information retrieval tasks commonly addressed in the context of historic research. History researchers were asked to describe in detail how they would proceed in searching for the information they need for completing these tasks. Through this procedure we aimed to investigate the different ways a historian can use to tackle a specific question, examine whether there exists a common research methodology, and the historic researchers? expectations and preferences. The insight gained from this investigation can be used for educational purposes, since it could be useful in the creation / development of a methodology for conducting research on historical information. Furthermore, the findings can be exploited in the context of organizing documents within historical source repositories, so as to facilitate the retrieval of documents by historians; finally the presented findings can serve as a preliminary requirement analysis phase for building tools that will enable historians to access more rapidly and fully the information they need.}, author = {Elena Torou and Akrivi Katifori and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @inbook {DBLP:reference/db/Skiadopoulos09, title = {Cardinal Direction Relationships}, booktitle = {Encyclopedia of Database Systems}, year = {2009}, pages = {305{\textendash}308}, doi = {10.1007/978-0-387-39940-9_45}, url = {https://doi.org/10.1007/978-0-387-39940-9_45}, author = {Spiros Skiadopoulos} } @book {DBLP:reference/db/2009, title = {Encyclopedia of Database Systems}, year = {2009}, publisher = {Springer US}, organization = {Springer US}, isbn = {978-0-387-35544-3}, doi = {10.1007/978-0-387-39940-9}, url = {https://doi.org/10.1007/978-0-387-39940-9}, editor = {Ling Liu and M. Tamer {\"O}zsu} } @inbook {benou2009a, title = {Encyclopedia of Information Science and Technology, Second Edition}, year = {2009}, pages = {1-7}, publisher = {IGI Global}, organization = {IGI Global}, chapter = {Exploiting Context in Mobile Applications}, abstract = {In the mobile and pervasive computing environment, software engineering should not treat diversity and mobility as problems to overcome, but seek methods of which it could take advantage instead. In these environments, the selection of purpose-oriented and timely information, tailored to user preferences and media characteristics will ensure an optimised information delivery. To this end, the context .the information that surrounds the human-computer interaction. plays a key role and is rapidly changing in mobile settings, and the understanding of it is indispensable for the application designers in order to choose, capture and exploit it. In this work, we present an architecture facilitating the collection of context information and its exploitation for optimized information delivery, within mobile and pervasive computing environments.}, doi = {10.4018/978-1-60566-026-4.ch236}, url = {https://www.igi-global.com/chapter/exploiting-context-mobile-applications/13774}, author = {Poulcheria Benou and Costas Vassilakis}, editor = {Mehdi Khosrow-Pour} } @conference {DBLP:conf/ssdbm/BourosSDSS09, title = {Evaluating Reachability Queries over Path Collections}, booktitle = {Scientific and Statistical Database Management, 21st International Conference, SSDBM 2009, New Orleans, LA, USA, June 2-4, 2009, Proceedings}, year = {2009}, pages = {398{\textendash}416}, doi = {10.1007/978-3-642-02279-1_29}, url = {https://doi.org/10.1007/978-3-642-02279-1_29}, author = {Panagiotis Bouros and Spiros Skiadopoulos and Theodore Dalamagas and Dimitris Sacharidis and Timos K. Sellis} } @conference {562, title = {EverLast: A Distributed Architecture for Preserving the Web}, booktitle = {Proceedings of the Joint Conference on Digital Libraries (JCDL)}, year = {2009}, month = {June}, address = {Austin, Texas}, author = {Avishek Anand and Srikanta Bedathur and Klaus Berberich and Ralf Schenkel and Christos Tryfonopoulos} } @conference {vas2009d, title = {A framework for adaptation in secure web services}, booktitle = {Proceedings of MCIS 2009}, year = {2009}, month = {9}, abstract = {In the context of service-oriented computing, the introduction of the Quality-of-Service (QoS) aspect leads to the need to adapt the execution of programs to the QoS requirements of the particular execution. This is typically achieved by finding alternate services that are functionally equivalent to the ones originally specified in the program and whose QoS characteristics closely match the requirements, and invoking the alternate services instead of the originally specified ones; the same approach can also be employed for tackling exceptions. The techniques proposed insofar, however, cannot be applied in a secure context, where data are encrypted and signed for the originally intended recipient. In this paper, we introduce a framework for facilitating adaptation in the context of secure SOA.}, author = {Costas Vassilakis and Christos Kareliotis} } @article {Vassilakis2009325, title = {A heuristics-based approach to reverse engineering of electronic services}, journal = {Information and Software Technology}, volume = {51}, number = {2}, year = {2009}, note = {cited By (since 1996) 1}, pages = {325-336}, abstract = {Since the beginning of the electronic era, public administrations and enterprises have been developing services, through which citizens, businesses and customers can conduct their transactions with the offering entity. Each electronic service contains a substantial amount of knowledge in the form help texts, rules of use or legislation excerpts, examples, validation checks, etc. This knowledge has been extracted from domain experts when the services were developed, especially in the phases of analysis and design, and was subsequently translated into software. In the latter format though, knowledge cannot be readily used in organizational processes, such as knowledge sharing and development of new services. In this paper, we present an approach for reverse engineering electronic services in order to create knowledge items of high levels of abstraction, which can be used in knowledge sharing environments as well as in service development platforms. The proposed approach has been implemented and configured to generate artifacts for the SmartGov service development platform. Finally, an evaluation of the proposed approach is presented to assess its efficiency regarding various aspects of the reverse engineering process. Β{\textcopyright} 2008 Elsevier B.V. All rights reserved.}, keywords = {Analysis and designs, Domain experts, e-government, electronic services, Government data processing, Help texts, In services, Knowledge engineering, Knowledge sharing, Levels of abstractions, Management, New services, Organizational knowledge, Organizational processes, Public administrations, Reengineering, Reverse engineering, Reverse engineering processes, Service developments, Validation checks}, doi = {10.1016/j.infsof.2008.04.003}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-56949100815\&partnerID=40\&md5=223ff82eddd9005b8e6f7fac1aa9c810}, author = {Costas Vassilakis and Giorgos Lepouras and Akrivi Katifori} } @article {583, title = {Information Filtering and Query Indexing for an Information Retrieval Model}, journal = {ACM Transactions on Information Systems (TOIS)}, volume = {27}, year = {2009}, pages = {1{\textendash}47}, author = {Christos Tryfonopoulos and Manolis Koubarakis and Yannis Drougas} } @article {Kareliotis2009284, title = {IQoS-aware exception resolution for BPEL processes: A middleware-based framework and performance evaluation}, journal = {International Journal of Web and Grid Services}, volume = {5}, number = {3}, year = {2009}, note = {cited By (since 1996) 0}, pages = {284-320}, abstract = {Web Services Business Process Execution Language (WS-BPEL) is widely used nowadays for specifying and executing composite business processes. During the execution, however, of such business processes, a number of faults stemming from the nature of SOA may occur. The WS-BPEL scenario designer must therefore use the provisions offered by WS-BPEL to catch these exceptions and resolve them. The system fault handler specification, however, is an additional task for the WS scenario designer, while the presence of such handlers within the scenario necessitates extra maintenance activities. In this paper, we propose a middleware-based framework for system exception resolution, which undertakes the tasks of failure interception, discovery of alternative services and their invocation. The process of selecting the alternative services can be driven by process consumer-specified Quality of Service (QoS) policy. Moreover, the middleware arranges for bridging syntactic differences between the originally invoked services and functionally equivalent replacements to it, by employing XSLT-based transformations. The middleware is deployed and maintained independently of the WS-BPEL scenarios, thus removing the need for specifying and maintaining system fault handlers within the scenarios. We also present performance measures, establishing that the overhead imposed by the addition of the proposed middleware layer is minimal. Copyright Β{\textcopyright} 2009, Inderscience Publishers.}, keywords = {Ad hoc networks, BPEL process, Exception handling, Exception resolution, Middleware, Performance metrics, QoS, Quality control, Quality of service, Scalability, Telecommunication services, Web services}, doi = {10.1504/IJWGS.2009.028346}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70349462474\&partnerID=40\&md5=4511b42fde076617cd6ac0139e3f588d}, author = {Christos Kareliotis and Costas Vassilakis and S. Rouvas and P. Georgiadis} } @conference {Vasiliadis2009395, title = {Performance evaluation of multicast routing over multilayer multistage interconnection networks}, booktitle = {Proceedings of the 2009 5th Advanced International Conference on Telecommunications, AICT 2009}, year = {2009}, note = {cited By (since 1996) 0}, month = {5}, pages = {395-403}, abstract = {Multilayer MINs have emerged mainly due to the increased need for routing capacity in the presence of multicast and broadcast traffic, their performance prediction and evaluation however has not been studied sufficiently insofar. In this paper, we use simulation to evaluate the performance of multilayer MINs with switching elements of different buffer sizes and under different offered loads. The findings of this paper can be used by MIN designers to optimally configure their networks. Β{\textcopyright} 2009 IEEE.}, keywords = {Broadcast traffic, Buffer sizes, Interconnection networks, Multicast routing, Multicasting, Multicasts, Multilayers, Multistage interconnection network, Network routing, Performance evaluation, Performance prediction, Switching elements}, doi = {10.1109/AICT.2009.72}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70349732883\&partnerID=40\&md5=e85525a7b36de8d84ea1ae52110ff1f9}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis and E. Glavas} } @conference {Christos2009271, title = {QoS-driven adaptation of BPEL scenario execution}, booktitle = {2009 IEEE International Conference on Web Services, ICWS 2009}, year = {2009}, note = {cited By (since 1996) 0}, month = {7}, pages = {271-278}, abstract = {BPEL/WSBPEL is the predominant approach for combining individual web services into integrated business processes, allowing for the specification of their sequence, control flow and data exchanges. BPEL however does not include mechanisms for considering the invoked services{\textquoteright} Quality of Service (QoS) parameters and thus BPEL scenarios can neither tailor their execution to the individual user{\textquoteright}s needs or adapt to the highly dynamic environment of the WEB, where new services may be deployed, old ones withdrawn or existing ones changing their QoS parameters. Moreover, infrastructure failures in the distributed environment of the web introduce an additional source of failures that must be considered in the context of QoS-aware service execution. In this work we propose a framework for addressing the issues identified above; the framework allows the users to specify the QoS parameters that they require and it undertakes the task of locating and invoking suitable services. Finally, the proposed framework intercepts and resolves faults occurring during service invocation, respecting the QoS restrictions specified by the consumer. Β{\textcopyright} 2009 IEEE.}, keywords = {Adaptive execution, BPEL, Control flows, Data exchange, Distributed environments, Dynamic environments, Infrastructure failures, Integrated business, New services, Performance evaliation, QoS parameters, Quality of service, Quality of Service parameters, Service execution, Service invocation, Web services}, doi = {10.1109/ICWS.2009.80}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70449472686\&partnerID=40\&md5=5303ebeff04a4e7a062f77209521d561}, author = {Christos Kareliotis and Costas Vassilakis and S. Rouvas and P. Georgiadis} } @article {540, title = {Rewiring Strategies for Semantic Overlay Networks}, journal = {Distributed and Parallel Databases (DAPD)}, volume = {26}, year = {2009}, pages = {181{\textendash}205}, abstract = {Semantic overlay networks cluster peers that are semantically, thematically or socially close into groups, by means of a rewiring procedure that is periodically executed by each peer. This procedure establishes new connections to similar peers and disregards connections to peers that are dissimilar. Retrieval effectiveness is then improved by exploiting this information at query time (as queries may address clusters of similar peers). Although all systems based on semantic overlay networks apply some rewiring technique, there is no comprehensive study showing the effect of rewiring on system{\textquoteright}s performance. In this work, a framework for studying the attribution of rewiring strategies in semantic overlay networks is proposed. A generic approach to rewiring is presented and several variants of this approach are reviewed and evaluated. We show how peer organisation is affected by the different design choices of the rewiring mechanism and how these choices affect the performance of the system overall (both in terms of communication overhead and retrieval effectiveness). Our experimental evaluation with real-word data and queries confirms the dependence between rewiring strategies and retrieval performance, and gives insights on the trade-offs involved in the selection of a rewiring strategy.}, keywords = {Information retrieval, peer-to-peer networks, rewiring strategies, semantic overlay networks}, author = {Paraskevi Raftopoulou and E.G.M. Petrakis and Christos Tryfonopoulos} } @conference {Vasiliadis200924, title = {Routing and performance evaluation of dual priority Delta networks under hotspot environment}, booktitle = {Proceedings - 2009 1st International Conference on Advances in Future Internet, AFIN 2009}, year = {2009}, note = {cited By (since 1996) 0}, month = {6}, pages = {24-30}, abstract = {Large swings in the demand for content are commonplace within the Internet. Although Multistage Interconnection Networks (MINs) are fairly flexible in handling varieties of traffic loads, their performance considerably degrades by hotspot traffic, especially at increasing size networks. As alleviation to the tree saturation problem, the prioritizing of packets is proposed leading to a scheme that natively supports multi priority traffic. In this paper the performance evaluation of double-buffered Delta Networks under single hotspot setups, with different offered loads, and 2-class routing traffic is presented and analyzed using simulation experiments. Performance comparison of dual vs. single priority scheme is outlined under hotspot environment, by calculating a universal performance factor, which effectively includes the importance aspect of each of the two most important performance metrics, namely packet throughput and delay. The findings of this paper can be used by MIN designers to optimally configure their networks. Β{\textcopyright} 2009 IEEE.}, keywords = {Computer simulation, Delta networks, Hot spot, Hotspot traffic, Interconnection networks, Internet, Multistage interconnection network, Multistage interconnection networks, Packet throughput, Performance comparison, Performance evaluation, Performance factors, Performance metrics, Priority schemes, Routing traffic, Saturation problems, Simulation, Simulation experiments, Traffic loads}, doi = {10.1109/AFIN.2009.12}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70350757772\&partnerID=40\&md5=f661e197254166cf6cf723546a5e5b88}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @proceedings {DBLP:conf/ssdbm/2009, title = {Scientific and Statistical Database Management, 21st International Conference, SSDBM 2009, New Orleans, LA, USA, June 2-4, 2009, Proceedings}, volume = {5566}, year = {2009}, publisher = {Springer}, isbn = {978-3-642-02278-4}, doi = {10.1007/978-3-642-02279-1}, url = {https://doi.org/10.1007/978-3-642-02279-1}, editor = {Marianne Winslett} } @article {DBLP:journals/tkde/KantereSS09, title = {Storing and Indexing Spatial Data in P2P Systems}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {21}, number = {2}, year = {2009}, pages = {287{\textendash}300}, doi = {10.1109/TKDE.2008.139}, url = {https://doi.org/10.1109/TKDE.2008.139}, author = {Verena Kantere and Spiros Skiadopoulos and Timos K. Sellis} } @conference {golem2009b, title = {Visualizing Hierarchies: Evaluating the Efficiency and Cognitive Effects of Six Visualization Techniques for Browsing and Management Tasks}, booktitle = {Information Visualization 2009, book of abstracts}, year = {2009}, month = {7}, abstract = {Hierarchical data structures are one of the most commonly used data structures in computer science, and therefore numerous methods and techniques have been proposed for their visualization. In this paper, we present our findings from a user study, in which a number of folder visualization environments were evaluated to assess (a) how efficiently a number of tasks can be performed within the different environments (b) the extent to which using a particular visualization may help the user acquire an accurate cognitive image of the hierarchy structure and its contents and (c) the overall user experience from using a particular visualization environment. The visualization environments considered are representative of major visualization paradigms (zoomable user interfaces, context+focus and space-filling), while both 2D and 3D environments have been included.}, author = {M. Golemati and Costas Vassilakis and Akrivi Katifori and Giorgos Lepouras and C. Halatsis} } @article {lep2008a1, title = {An active blackboard for service discovery, composition and execution}, journal = {International Journal of Electronic Governance}, volume = {1}, number = {3}, year = {2008}, pages = {275 - 295}, publisher = {Inderscience Publishers}, abstract = {Organisations are turning to customer-centric electronic services, oriented to servicing customers{\textquoteright} life-events. This development requires methods for automatically locating and synthesising individual services to compose complex ones that will service the customer{\textquoteright}s life-events, since manual composition, either at the customer or the organisation side, incurs functional, economic and technical problems. In this paper we present an active blackboard architecture, which automates the task of service composition based on the semantics of individual services and data dependencies between them. The blackboard incorporates registries, which facilitate service discovery and an execution engine that arranges for dynamic service composition and execution.}, keywords = {blackboard architecture, e-government, e-services, electronic governance, electronic services, ontologies, semantics, service composition}, doi = {10.1504/IJEG.2008.020450}, author = {Giorgos Lepouras and Costas Vassilakis and Anya Sotiropoulou and Dimitrios Theotokis and Akrivi Katifori} } @booklet {569, title = {Anonymous and Censorship-resistant Content-sharing in Unstructured Overlays}, year = {2008}, author = {Michael Backes and Marek Hamerlik and Alessandro Linari and Matteo Maffei and Christos Tryfonopoulos and Gerhard Weikum} } @conference {586, title = {Approximate Information Filtering in Peer-to-Peer Networks}, booktitle = {Proceedings of the 9th Web Information Systems Engineering (WISE) Conference}, year = {2008}, month = {September}, address = {Auckland, New Zealand}, author = {Christian Zimmer and Christos Tryfonopoulos and Klaus Berberich and Manolis Koubarakis and Gerhard Weikum} } @conference {daradim2008, title = {A Drupal CMS Module for Managing Museum Collections}, booktitle = {International Symposium on Information \& communication technologies in cultural heritage}, year = {2008}, month = {10}, abstract = {Digitization efforts and web presentations are currently on-going in many museums, archives, libraries and culture heritage institutions in general, exploiting the advent of WWW and digitization technologies. The main benefits from these efforts are exhibit cataloguing, their effective management, preservation and showcasing, and their presentation to the public through the WWW. However, many museums, especially the smaller ones, cannot afford a commercial product and resort to using simple static web pages for their web presence and exhibit presentation. Content Management Systems (CMS), especially open-source ones which come with practically zero-cost, are more and more frequently adopted by museums to create and maintain their website, since they simplify the creation and editing of the web pages and may be used by non-computer experts. In this work we present a module for the Drupal CMS, which provides functionality for (a) Database schema extension to accommodate museum exhibit and collection information (b) Digital exhibit representation (DER) management. (c) Provision of administration pages through which the museum personnel may enter and manage exhibit and collection information (d) WWW scowcasing and (e) Batch data import/export, to facilitate information exchange with other museums.}, author = {I. Daradimos and Costas Vassilakis and Akrivi Katifori} } @conference {vassiliadis2008d, title = {Evaluation Study of a Wireless Multimedia Traffic-Oriented Network Model}, booktitle = {INTERNATIONAL ELECTRONIC CONFERENCE ON COMPUTER SCIENCE. AIP Conference Proceedings, Volume 1060}, year = {2008}, month = {7}, pages = {379-384}, abstract = {In this paper, a wireless multimedia traffic-oriented network scheme over a fourth generation system (4-G) is presented and analyzed. We conducted an extensive evaluation study for various mobility configurations in order to incorporate the behavior of the IEEE 802.11b standard over a test-bed wireless multimedia network model. In this context, the Quality of Services (QoS) over this network is vital for providing a reliable high-bandwidth platform for data-intensive sources like video streaming. Therefore, the main issues concerned in terms of QoS were the metrics for bandwidth of both dropped and lost packets and their mean packet delay under various traffic conditions. Finally, we used a generic distance-vector routing protocol which was based on an implementation of Distributed Bellman-Ford algorithm. The performance of the test-bed network model has been evaluated by using the simulation environment of NS-2.}, doi = {10.1063/1.3037098}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @conference {Christos2008248, title = {Exception resolution for BPEL processes: A middleware-based framework and performance evaluation}, booktitle = {Proceedings of the 10th International Conference on Information Integration and Web-based Applications and Services, iiWAS 2008}, year = {2008}, note = {cited By (since 1996) 0}, month = {12}, pages = {248-256}, abstract = {WS-BPEL is widely used nowadays for specifying and executing composite business processes within the Service Oriented Architecture (SOA). During the execution however, of such business processes, a number of faults stemming from the nature of SOA (e.g. network or server failures) may occur. The WS-BPEL scenario designer must therefore use the provisions offered by WS-BPEL to catch these exceptions and resolve them, usually by invoking some equivalent web service that is expected to be reachable and available. System fault handler specification is though an additional task for the WS scenario designer, while the presence of such handlers within the scenario necessitates extra maintenance activities, as new alternate services emerge or some of the specified ones are withdrawn. In this paper, we propose a middleware-based framework for system exception resolution, which undertakes the tasks of failure interception, discovery of alternate services and their invocation. The middleware is deployed and maintained independently of the WS-BPEL scenarios, removing thus the need for specifying and maintaining system fault handlers within the scenarios. We also present performance measures, establishing that the overhead imposed by the addition of the proposed middleware layer is minimal. Β{\textcopyright} 2008 ACM.}, keywords = {Ad hoc networks, Business Process, Exception handling, Information retrieval, Information services, Maintenance activity, Middleware, Middleware layer, Performance evaluation, Performance measure, Performance metrics, Quality control, Quality of service, Quality of service (QoS), Scalability, Service oriented architecture (SOA), System faults, Telecommunication services, Web services, WS-BPEL}, doi = {10.1145/1497308.1497355}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70349146138\&partnerID=40\&md5=9a5231fe52fffef11707efd4f3489a37}, author = {Christos Kareliotis and Costas Vassilakis and S. Rouvas and P. Georgiadis} } @conference {574, title = {Exploiting Correlated Keywords to Improve Approximate Information Filtering}, booktitle = {Proceedings of the 31st Annual International ACM SIGIR Conference}, year = {2008}, month = {July}, address = {Singapore}, author = {Christian Zimmer and Christos Tryfonopoulos and Gerhard Weikum} } @conference {Mateevitsi2008451, title = {A game-engine based virtual museum authoring and presentation system}, booktitle = {Proceedings - 3rd International Conference on Digital Interactive Media in Entertainment and Arts, DIMEA 2008}, year = {2008}, note = {cited By (since 1996) 0}, month = {9}, pages = {451-457}, abstract = {In this paper we present a system that facilitates virtual museum development and usage. The system is based on a game engine, ensuring thus minimal cost and good performance, and includes provisions that enable museum curators design the virtual museum without any specialized knowledge. Besides visual and auditory information, museum curators may also provide metadata which provide additional information to the visitor, while they can be also exploited for searching for exhibits with certain properties. A guide is also included in the museum, to present additional information to the visitors and aid them throughout their tour. Copyright 2008 ACM.}, keywords = {Authoring environment, Game engines, Game theory, Metadata, Minimal costs, Museum guide, Presentation systems, Specialized knowledge, Virtual museum}, doi = {10.1145/1413634.1413714}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-62849090231\&partnerID=40\&md5=2ba9707b8125ec8f1cacaad99b611342}, author = {Mateevitsi, V. and Sfakianos, M. and Giorgos Lepouras and Costas Vassilakis} } @conference {595, title = {iCluster: a Self-Organizing Overlay Network for P2P Information Retrieval}, booktitle = {Proceedings of 30th European Conference on Information Retrieval (ECIR)}, year = {2008}, month = {March}, address = {Glasgow, Scotland}, abstract = {We present iCluster, a self-organizing peer-to-peer overlay network for supporting full-fledged information retrieval in a dynamic environment. iCluster works by organizing peers sharing common interests into clusters and by exploiting clustering information at query time for achieving low network traffic and high recall. We define the criteria for peer similarity and peer selection, and we present the protocols for organizing the peers into clusters and for searching within the clustered organization of peers. iCluster is evaluated on a realistic peer-to-peer environment using real-world data and queries. The results demonstrate significant performance improvements (in terms of clustering efficiency, communication load and retrieval accuracy) over a state-of-the-art peer- to-peer clustering method. Compared to exhaustive search by flooding, iCluster exchanged a small loss in retrieval accuracy for much less message flow.}, author = {Paraskevi Raftopoulou and E.G.M. Petrakis} } @conference {Vasiliadis200823, title = {Improving performance of finite-buffered blocking delta networks with 2-class priority routing through asymmetric-sized buffer queues}, booktitle = {Proceedings - 4th Advanced International Conference on Telecommunications, AICT 2008}, year = {2008}, note = {cited By (since 1996) 1}, month = {6}, pages = {23-29}, abstract = {In this paper the performance of asymmetric-sized finite-buffered Delta Networks with 2-class routing traffic is presented and analyzed in the uniform traffic conditions under various loads using simulations. We compare the performance of 2-class priority mechanism against the single priority one, by gathering metrics for the two most important network performance factors, namely packet throughput and delay. We also introduce and calculate a universal performance factor, which includes the importance aspect of each of the above main performance factors. We found that the use of asymmetric-sized buffered systems leads to better exploitation of network capacity, while the increments in delays can be tolerated. The goal of this paper is to help network designers in performance prediction before actual network implementation and in understanding the impact of each parameter factor. Β{\textcopyright} 2008 IEEE.}, keywords = {Computer networks, Delta networks, International conferences, Performance factors}, doi = {10.1109/AICT.2008.13}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-50949090335\&partnerID=40\&md5=1a38fdae7e54da27ace165ed90b5a386}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @conference {549, title = {Information Retrieval and Filtering over Self-Organising Digital Libraries}, booktitle = {Proceedings of the 12th European Conference on Research and Advanced Technology for Digital Libraries (ECDL)}, year = {2008}, month = {September}, address = {Aarhus, Denmark}, author = {Paraskevi Raftopoulou and E.G.M. Petrakis and Christos Tryfonopoulos and Gerhard Weikum} } @article {vas2008d, title = {An Integrated Environment for Cataloguing and Online Presentation of Museum Exhibits}, journal = {DESIDOC Journal of Library and Information Technology}, volume = {28(4)}, year = {2008}, pages = {72-78}, abstract = {The paper presents an integrated environment which enables museum personnel to catalogue and at the same time publish online museum exhibits. The system is based on international standards and is highly customisable to cater the needs of a variety of museum types. Moreover, the underlying database allows storing for the same exhibit documentations for different audiences and in multiple languages, while it is extendable to accommodate new media types, languages, exhibits and information categories. The administrative part of the environment permits the restriction of certain functions to specific personnel roles, enforcing thus a general museum security policy regarding access to and modification of information. The environment presented is currently in use at the Athens University History Museum.}, author = {Costas Vassilakis and Akrivi Katifori and I. Daradimos and Giorgos Lepouras} } @inbook {gol2009a, title = {Intelligent User Interfaces: Adaptation and Personalization Systems and Technologies}, year = {2008}, pages = {188{\textendash}204}, publisher = {IGI Publishing}, organization = {IGI Publishing}, chapter = {Context and Adaptivity-Driven Visualization Method Selection}, abstract = {Novel and intelligent visualization methods are being developed in order to accommodate user searching and browsing tasks, including new and advanced functionalities. Besides, research in the field of user modeling is progressing in order to personalize these visualization systems, according to its users{\textquoteright} individual profiles. However, employing a single visualization system, may not suit best any information seeking activity. In this paper we present a visualization environment, which is based on a visualization library, i.e. is a set of visualization methods, from which the most appropriate one is selected for presenting information to the user. This selection is performed combining information extracted from the context of the user, the system configuration and the data collection. A set of rules inputs such information and assigns a score to all candidate visualization methods. The presented environment additionally monitors user behavior and preferences to adapt the visualization method selection criteria.}, author = {M. Golemati and Costas Vassilakis and Akrivi Katifori and Giorgos Lepouras and C. Halatsis}, editor = {C. Mourlas and P. Germanakos} } @conference {Golemati2008106, title = {An interview-based user study on the use of visualizations for folder browsing}, booktitle = {Proceedings of the International Conference on Information Visualisation}, year = {2008}, note = {cited By (since 1996) 0}, month = {7}, pages = {106-112}, abstract = {Hierarchically structured data collections often need to be visualized for the purposes of digital information management and presentation. File browsing, in particular, has an inherent hierarchical structure and plays an important role in the context of Personal Information Management (PIM). A multitude of file browsers are nowadays available, offering different functionalities, while users adopt diverse practices and habits for browsing activities. In this paper, we investigate these aspects to obtain insights into their advantages and disadvantages and suggest solutions in the area of PIM, as well as in other domains employing similar visualization paradigms. The presented study focuses on the two most widespread visualizations used by file browsers, the indented list and zoomable interface paradigms, and assesses their effectiveness for various tasks and contexts, both by exploiting results on existing evaluations on hierarchy visualizations and folder hierarchy visualizations in particular, and by conducting an interviewbased user study. Β{\textcopyright} 2008 IEEE.}, keywords = {Administrative data processing, File browser visualization, Indented list visualization, Information analysis, Information management, Information science, Intermodulation, Intermodulation measurement, International conferences, Management, Management information systems, Telecommunication services, User study, Windows explorer}, doi = {10.1109/IV.2008.90}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-51749097531\&partnerID=40\&md5=66afc30e74191773d1c950ac83ba9ac7}, author = {M. Golemati and Akrivi Katifori and E.G. Giannopoulou and I. Daradimos and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @conference {596, title = {A Measure for Cluster Cohesion in Semantic Overlay Networks}, booktitle = {Proceedings of the 6th International Workshop on Large-Scale Distributed Systems for Information Retrieval (LSDS-IR)}, year = {2008}, month = {October}, publisher = {ACM}, organization = {ACM}, address = {Napa Valley, California}, abstract = {Semantic overlay networks cluster peers that are semantically, thematically or socially close into groups by means of a rewiring procedure that is periodically executed by each peer. Rewiring proceeds by establishing new connections to similar peers, and by discarding connections that are out- dated or pointing to dissimilar peers. This process aims at improving cluster quality (how well peers with similar con- tent are clustered together) and by this, at improving the flow of information in the network by reducing the number of messages that are exchanged. Therefore, measuring the quality of clustering is an important issue by itself. This is exactly the issue this work is dealing with. In this paper, we introduce a new clustering measure that takes into account the whole neighbourhood of a peer (rather than its direct neighbours) thus, providing better insight on the quality of the underlying clustered organisation. Our experimental evaluation with real-word data and queries confirms our assumption that the new measure is better suited for measuring clustering quality than other known measures, such as the (generalised) clustering coefficient.}, author = {Paraskevi Raftopoulou and E.G.M. Petrakis} } @article {DBLP:journals/tkde/PolyzotisSVSF08, title = {Meshing Streaming Updates with Persistent Data in an Active Data Warehouse}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {20}, number = {7}, year = {2008}, pages = {976{\textendash}991}, doi = {10.1109/TKDE.2008.27}, url = {https://doi.org/10.1109/TKDE.2008.27}, author = {Neoklis Polyzotis and Spiros Skiadopoulos and Panos Vassiliadis and Alkis Simitsis and Nils-Erik Frantzell} } @article {Vassilakis2008, title = {Mobile and context-aware e-commerce: Issues, challenges and research directions}, journal = {Journal of Electronic Commerce in Organizations}, volume = {6}, number = {1}, year = {2008}, pages = {i-iv}, abstract = {Electronic commerce, nowadays, is trying to extend its target audience and elevate the quality of services offered to end-users. Two important directions towards meeting these goals are the embracement of mobile users, whose number grows following the advent of communication technologies, and the inclusion of context-aware features in the delivered services to improve the efficiency of the dialogues between users and systems. The context taken into account may involve characteristics regarding the human user, the geographical location and the time of access, the devices employed to access the service, the network through which the user communicates with the system, the nature of the transaction carried out and so forth. It is clear that the development and successful operation of mobile and context-aware e-commerce introduce new challenges. In order to tackle such challenges, new methodologies, tools, architectures and platforms should be made available to assist analysts, designers, developers and operators in handling the various phases of the Mobile and Context-Aware E-Commerce Services (MCACS) lifecycle.}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-56649115725\&partnerID=40\&md5=8375300b820641c0897304ece76039d9}, author = {Costas Vassilakis and Giorgos Lepouras and Spiros Skiadopoulos} } @conference {katifori2008e, title = {Ontologies as Tools for Historians}, booktitle = {International Symposium on Information \& communication technologies in cultural heritage}, year = {2008}, month = {10}, abstract = {Ontologies have been proven invaluable tools in areas like the semantic web and personal information management. There have been many research efforts to create ontologies and supporting tools for Natural Sciences and Biology in particular (e.g. the GO (http://www.geneontology.org/) ontology and supporting tools). However, the domain of History, the science of studying, recording and organizing the knowledge of the past, has yet to benefit from adopting ontologies. In this work, we present our findings in this area, focusing on the aspects of ontology modeling and ontology visualization.}, author = {Akrivi Katifori and Costas Vassilakis} } @conference {566, title = {P2P Information Retrieval and Filtering with MAPS}, booktitle = {Proccedings of the IEEE International Conference on Peer-to-Peer Computing (P2P)}, year = {2008}, month = {September}, address = {Aachen, Germany}, author = {Christian Zimmer and Johannes Heinz and Christos Tryfonopoulos and Gerhard Weikum} } @conference {Vasiliadis200890, title = {Performance Evaluation of Distance Vector Routing Protocol on a Wireless Circular Model}, booktitle = {Proceedings of the IEEE sponsored International Joint Conference CISSE 2007}, year = {2008}, month = {12}, pages = {323-328}, publisher = {Springer Netherlands}, organization = {Springer Netherlands}, abstract = {In this paper, a wireless Circular Model over a generic distance-vector routing protocol is presented and analyzed. The performance of this model over the Distance Vector protocol, which is an implementation of Distributed Bellman-Ford algorithm, has been evaluated by using the simulation environment of NS-2. We conducted an extensive evaluation study for various mobility schemes in order to incorporate the behavior of nodes and the routing protocol in a real-life hotspot situation In the test-bed model, while the number of source nodes was allowed to arbitrarily vary, there was exactly one destination node, closely modeling thus real-life situations where a single hotspot/access point exists. Finally, different constant bit rates (CBR) were used in order to estimate the throughput of receiving, dropping rates, the number of lost packets, as well as the average packet delay under various traffic conditions. This study is aimed to help wireless network designers in choosing the best suited routing protocols for their networks, through making explicit performance figures for common network setups.}, doi = {10.1007/978-1-4020-8737-0}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis}, editor = {Tarek Sobh and Khaled Elleithy and Ausif Mahmood and Mohammad A. Karim} } @conference {Katifori2008a1, title = {Personal Ontology Creation and Visualization for a Personal Interaction Management System}, booktitle = {Proceedings of PIM, CHI 2008}, year = {2008}, month = {4}, abstract = {Ontologies offer a flexible and expressive layer of abstraction, very useful for capturing the semantics of information repositories and facilitating their retrieval either by the user or by the system to support user tasks. This work presents an ontology-based user profiler, in the context of a Personal Interaction Management System (PIMS). The profiler, based on an ontology of the users? domain, enables them to create their personal ontology by initially choosing one of the available template ontologies as a starting point, which they subsequently populate and customize. The profiler employs a web interface which allows users to populate their personal ontology through forms, hiding ontology complexities and peculiarities. Forms are dynamically generated through ontology views, which are specified by ontology designers.}, author = {Akrivi Katifori and Costas Vassilakis and I. Daradimos and Giorgos Lepouras and Yannis Ioannidis and Alan Dix and Antonella Poggi and Tiziana Catarci} } @conference {Vasiliadis200856, title = {Routing and performance analysis of double-buffered omega networks supporting multi-class priority traffic}, booktitle = {Proc. - The 3rd Int. Conf. Systems and Networks Communications, ICSNC 2008 - Includes I-CENTRIC 2008: Int. Conf. Advances in Human-Oriented and Personalized Mechanisms, Technologies, and Services}, year = {2008}, note = {cited By (since 1996) 1}, month = {10}, pages = {56-63}, abstract = {In this paper the modeling of Omega Networks supporting multi-class routing traffic is presented and their performance is analyzed. We compare the performance of multi-class priority mechanism against the single priority one, by gathering metrics for the two most important network performance factors, namely packet throughput and delay under uniform traffic conditions and various offered loads, using simulations. Moreover, two different test-bed setups were used in order to investigate and analyze the performance of all priority-class traffic, under different Quality of Service (QoS) configurations. In the considered environment, Switching Elements (SEs) that natively support multi-class priority routing traffic are used for constructing the MIN, while we also consider double-buffered SEs, two configuration parameters that have not been addressed insofar. The rationale behind introducing a multiple-priority scheme is to provide different QoS guarantees to traffic from different applications, which is a highly desired feature for many IP network operators, and particularly for enterprise networks. Β{\textcopyright} 2008 IEEE.}, keywords = {Computer networks, Configuration parameters, Enterprise networks, Ip networks, Metropolitan area networks, Network performances, Packet throughputs, Performance analyses, Priority schemes, Qos guarantees, Quality of service, Routing traffics, Set-ups, Systems engineering, Uniform traffics}, doi = {10.1109/ICSNC.2008.10}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-58149096344\&partnerID=40\&md5=11b2d45a47554d3556034866c2f3ac49}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis and E. Glavas} } @conference {Katifori2008133, title = {Selected results of a comparative study of four ontology visualization methods for information retrieval tasks}, booktitle = {Proceedings of the 2nd International Conference on Research Challenges in Information Science, RCIS 2008}, year = {2008}, note = {cited By (since 1996) 0}, month = {6}, pages = {133-140}, abstract = {The need for effective ontology visualization for design, management and browsing has arisen as a result of the progress in the areas of Semantic Web and Personal Information Management. There are several ontology visualizations available through existing ontology management tools, but not as many evaluations to determine their advantages and disadvantages and their suitability for various ontologies and user groups. This work presents selected results of an evaluation of four visualization methods in ProtΓ{\textcopyright}gΓ{\textcopyright}.}, keywords = {Communication, Comparative studies, Information management, Information retrieval, Information science, Information services, Information theory, Management, Management information systems, Ontology, Ontology managements, Personal Information managements, Semantic Web, Telecommunication services, User groups, User interfaces, Visualization, visualization methods}, doi = {10.1109/RCIS.2008.4632101}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-57349172797\&partnerID=40\&md5=1f36a9a0febecb929cd7904c84004143}, author = {Akrivi Katifori and Elena Torou and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @conference {Katifori200832, title = {Supporting research in historical archives: Historical information visualization and modeling requirements}, booktitle = {Proceedings of the International Conference on Information Visualisation}, year = {2008}, note = {cited By (since 1996) 0}, month = {7}, pages = {32-37}, abstract = {The on-going progress in the area of digital libraries has lead to the beginning of a digitization effort in Historical Archives, as well. The requirements of historical research, which works with histories of entities and incomplete information, create the need for supplementary tools to support users in handling the digitized content. This work is based on a user study of historian information retrieval methods in order to create a set of tools for the context of historical archives, which will facilitate historical data storage, management and visualization. Β{\textcopyright} 2008 IEEE.}, keywords = {Data visualization, Digital libraries, Heuristics, Historical archive, Information analysis, Information management, Information retrieval, Information science, Information services, Information systems, International conferences, Libraries, Ontology, Search engines, Visualization}, doi = {10.1109/IV.2008.70}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-51749114860\&partnerID=40\&md5=a5b3e7f74314d5651816424c11e6cbc1}, author = {Akrivi Katifori and Elena Torou and Costas Vassilakis and C. Halatsis} } @conference {katifori2008b, title = {Using Spreading Activation through Ontologies to Support Personal Information Management}, booktitle = {Proceedings of CSKGOI, within IUI 2008}, year = {2008}, month = {1}, abstract = {Recent research in the domain of Personal Information Management has recognized the need for a paradigm shift towards a more activity-oriented system. Ontologies, as semantic networks with a structure not dissimilar to the one used by the human brain for storing long-term knowledge, may be very useful as the basis of such a system. This work proposes the use of spreading activation over ontologies in order to provide to a task-based system and its associated tools with methods to record semantics related to documents and tasks and to support user context inference.}, url = {http://ceur-ws.org/Vol-323/paper05.pdf}, author = {Akrivi Katifori and Costas Vassilakis and Alan Dix} } @conference {Daradimos2008141, title = {WhereRU: GPS position reporting and a personal ontology as a virtual community utility}, booktitle = {Proceedings of the 2nd International Conference on Research Challenges in Information Science, RCIS 2008}, year = {2008}, note = {cited By (since 1996) 0}, month = {6}, pages = {141-146}, abstract = {The recent progress of the World Wide Web has created new needs for information sharing in virtual communities. WhereRU is a multiuser GPS position reporting system that allows users to make their location publicly available as well as associate it with information on places, persons and events that may later also serve as reminders of the their experiences when traveling.}, keywords = {Communication, Global positioning system, Gps positions, Information science, Information sharing, Internet, Multiuser, Ontology, Personal ontologies, Position reporting, Recent progresses, Reporting systems, Satellite navigation aids, Virtual communities, Virtual reality, Web community, World Wide Web}, doi = {10.1109/RCIS.2008.4632102}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-57349094004\&partnerID=40\&md5=4eaed4757acf5c4da8b292275b92a73a}, author = {I. Daradimos and Akrivi Katifori and Costas Vassilakis} } @proceedings {DBLP:conf/ssd/2007, title = {Advances in Spatial and Temporal Databases, 10th International Symposium, SSTD 2007, Boston, MA, USA, July 16-18, 2007, Proceedings}, volume = {4605}, year = {2007}, publisher = {Springer}, isbn = {978-3-540-73539-7}, doi = {10.1007/978-3-540-73540-3}, url = {https://doi.org/10.1007/978-3-540-73540-3}, editor = {Dimitris Papadias and Donghui Zhang and George Kollios} } @conference {kalikakis2007b, title = {An Approach for re-engineering the Taxation Process to Support Participatory Decisions on Tax Budget Allocation}, booktitle = {Proceedings of the 1st International Conference on Methodologies, Technologies and Tools enabling e-Government}, year = {2007}, month = {9}, abstract = {The tax collection process has been described as a bureaucratic one, that confines citizen involvement to the role of passive fulfillment of administrative and financial obligations. Active citizen participation, in the form of some political say on the allocation of collected taxes which could potentially improve and further legitimize tax collection, is not a part of the traditional taxation model. In this paper we describe a new taxation model which, in the spirit of participatory budgeting approaches, supports active citizens? participation on decision making regarding tax funds allocation.}, author = {M. Kalikakis and D. Gouscos and Costas Vassilakis and P. Georgiadis} } @article {557, title = {Architectural Alternatives for Information Filtering in Structured Overlay Networks}, journal = {IEEE Internet Computing}, volume = {11}, year = {2007}, pages = {24-34}, author = {Christos Tryfonopoulos and Christian Zimmer and Manolis Koubarakis and Gerhard Weikum} } @article {DBLP:journals/tkde/SkiadopoulosSSK07a, title = {Correction to "A Family of Directional Relation Models for Extended Objects"}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {19}, number = {10}, year = {2007}, pages = {1448}, doi = {10.1109/TKDE.2007.190653}, url = {https://doi.org/10.1109/TKDE.2007.190653}, author = {Spiros Skiadopoulos and Nikos Sarkas and Timos K. Sellis and Manolis Koubarakis} } @conference {KatiforiGVLH07, title = {Creating an Ontology for the User Profile: Method and Applications}, booktitle = {RCIS}, year = {2007}, month = {4/2007}, pages = {407{\textendash}412}, abstract = {User profiling is commonly employed nowadays to enhance usability as well as to support personalization, adaptivity and other user-centric features. Insofar, application designers model user profiles mainly in an ad-hoc manner, hindering thus application interoperability at the user profile level, increasing the amount of work to be done and the possibility of errors or omissions in the profile model. This work aims at creating a user profile ontology that incorporates concepts and properties used to model the user profile. Existing literature, applications and ontologies related to the domain of user context and profiling have been taken into account in order to create a general, comprehensive and extensible user model. This ontology can be used as a reference model, in order to alleviate the aforementioned issues. The model, available for download, is exemplified through its application in two different areas, personal information management and adaptive visualization.}, author = {Akrivi Katifori and M. Golemati and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @article {Lepouras200779, title = {Domain expert user development: The smartgov approach}, journal = {Communications of the ACM}, volume = {50}, number = {9}, year = {2007}, month = {sep}, pages = {79-83}, publisher = {Association for Computing Machinery (ACM)}, abstract = {SmartGov project funded by the European Union is a knowledge-based platform that assists pubic-sector employees with suitable expertise to generate online transaction devices by simplifying service development, maintenance, and integration with installed information technology systems. The project delivers intelligent e-forms development and maintenance environment and associated framework for e-government services. SmartGov address various problems faced by the stakeholders while implementing e-services such as limited view of domain experts, lost information, complexity of creating e-forms, and inadequate access. In a SmartGov approach, the implicit knowledge is made explicit in the form of documentation and data validation rules. The central concept of SmartGov is the transaction service element (TSE) that contain metadata and domain knowledge.}, keywords = {Data validation, Documentation, Information services, Information technology, Knowledge based platform, Knowledge based systems, Metadata, Online systems, Project management, Transaction service element (TSE)}, doi = {10.1145/1284621.1284623}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-34548411694\&partnerID=40\&md5=43df285b5a79ef731b3466106642af9f}, author = {Giorgos Lepouras and Costas Vassilakis and C. Halatsis and P. Georgiadis} } @conference {543, title = {Efficient Search and Approximate Information Filtering in a Distributed Peer-to-Peer Environment of Digital Libraries}, booktitle = {Proceedings of the DELOS Conference on Digital Libraries}, year = {2007}, month = {February}, address = {Pisa, Italy}, author = {Christian Zimmer and Christos Tryfonopoulos and Gerhard Weikum} } @inbook {vas2007a, title = {Encyclopedia of Digital Government}, year = {2007}, pages = {1174{\textendash}1179}, publisher = {IGI Publishing}, organization = {IGI Publishing}, chapter = {The Lifecycle Of Transactional Services}, abstract = {Transactional services are an indispensible part of e-government, since provision of services to citizens and enterprises,as well as the interaction between the government and citizens-enterprises are modelled mainly through such services. Latest quantifications, however, show that the development of such services lags behind as compared both to the expectations of citizens-enterprises and to the efforts made by governments. This can be attributed, amongst other reasons, to the "traditional" approach to electronic service development, which treats each electronic service as an isolated software project. In this paper, we propose an e-service development platform, which covers the whole lifecycle of transactional services and facilitates the analysis, development, deployment and maintenance of these services.}, doi = {10.4018/978-1-59140-789-8.ch177}, author = {Costas Vassilakis and Giorgos Lepouras}, editor = {Ari-Veikko Anttiroiko and Matti Malkia} } @inbook {lep2007a, title = {Encyclopedia of Digital Government}, year = {2007}, pages = {1413{\textendash}1417}, publisher = {IGI Publishing}, organization = {IGI Publishing}, chapter = {Reusability In Governmental Electronic Services}, abstract = {Reusability is the degree to which a software component or other work can be used in more than one programs or software systems. e-Government is a prosperous area for the application of reusability, since the services offered to citizens from the same administration, or even different administrations, have common portions that can be developed only once and reused wherever appropriate. In this paper we present the design and implementation of an electronic service development environment which offers the potential to reuse components that have already been implemented, for the realization of new services.}, doi = {10.4018/978-1-59140-789-8.ch216}, author = {Giorgos Lepouras and Costas Vassilakis}, editor = {Ari-Veikko Anttiroiko and Matti Malkia} } @conference {DBLP:conf/icws/KareliotisVG07, title = {Enhancing BPEL scenarios with Dynamic Relevance-Based Exception Handling}, booktitle = {ICWS}, year = {2007}, month = {7}, pages = {751-758}, abstract = {Web services have become the key technology in business processes management. Business processes can be self-contained or be composed from sub-processes; the latter category is typically specified using the Web Services Business Process Execution Language (WS-BPEL) and executed by a Web Services Orchestrator (WSO). During the execution however of such a composite service, a number of faults stemming from the distributed nature of the SOA architecture, e.g. network or server failures may occur. WS-BPEL includes provisions for exception handling, which can be exploited for detecting such failures; once detected, a failure can be resolved by invoking alternate web service implementations that perform the same business task as the failed one. However, the inclusion of such provisions is a tedious assignment for the business process designer, while additional effort would be required to maintain the BPEL scenarios in cases that some alternate WS implementations cease to exist or new ones are introduced. In our research we are developing a framework for automating handling of that kind of exceptions. The proposed solution employs a pre-processor that enhances BPEL scenarios with code that detects failures, discovers alternate WS implementations and invokes them, fully thus resolving the exception. Alternate WS implementation discovery is based on service relevance, which takes into account both functional and qualitative properties of web services.}, doi = {10.1109/ICWS.2007.86}, author = {Christos Kareliotis and Costas Vassilakis and P. Georgiadis} } @conference {Golemati200793, title = {Evaluating the significance of the windows explorer visualization in personal information management browsing tasks}, booktitle = {Proceedings of the International Conference on Information Visualisation}, year = {2007}, note = {cited By (since 1996) 0}, month = {7}, pages = {93-98}, abstract = {The visualization of hierarchies is very important for digital information management and presentation systems. Especially in the context of Personal Information Management, file browsers play a very important role. Currently the most common file browser visualizations are Windows Explorer and the simple zoomable visualization offered by Microsoft Windows. This work explores the issue of file browser visualization through a user study based on inter-views and an experiment. Β{\textcopyright} 2007 IEEE.}, keywords = {Data reduction, File browser visualization, Hierarchical systems, Indented list visualization, Information analysis, User study, Web browsers, Windows explorer}, doi = {10.1109/IV.2007.46}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-35348919670\&partnerID=40\&md5=f35f306d4063ee2e91e3c573f4ed5d8a}, author = {M. Golemati and Akrivi Katifori and E.G. Giannopoulou and I. Daradimos and Costas Vassilakis} } @article {DBLP:journals/tkde/SkiadopoulosSSK07, title = {A Family of Directional Relation Models for Extended Objects}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {19}, number = {8}, year = {2007}, pages = {1116{\textendash}1130}, doi = {10.1109/TKDE.2007.1046}, url = {https://doi.org/10.1109/TKDE.2007.1046}, author = {Spiros Skiadopoulos and Nikos Sarkas and Timos K. Sellis and Manolis Koubarakis} } @conference {KatiforiVTLHD07, title = {Historical Archive Ontologies Requirements, Modeling and Visualization}, booktitle = {RCIS}, year = {2007}, month = {4}, pages = {401-406}, abstract = {Most ontology development methodologies and tools for ontology management deal with ontology snapshots, i.e. they model and manage only the most recent version of ontologies, which is inadequate for contexts where the history of the ontology is of interest, such as historical archives. This work presents a set of requirements for the modeling and visualization of a temporal ontology used as a tool for the representation of historical information. In accordance to these requirements, a visualization plug-in was designed and implemented, featuring a set of tools that enable users to efficiently examine ontology temporal characteristics such as class and instance evolution along the timeline.}, author = {Akrivi Katifori and Costas Vassilakis and Elena Torou and Giorgos Lepouras and C. Halatsis and I. Daradimos} } @article {Vassilakis2007113, title = {A knowledge-based approach for developing multi-channel e-government services}, journal = {Electronic Commerce Research and Applications}, volume = {6}, number = {1}, year = {2007}, note = {cited By (since 1996) 0}, pages = {113-124}, abstract = {Having realised the benefits resulting from delivering on-line public services in the context of electronic government, administrations strive to extend the spectrum of services offered to citizens and enterprises, as well as to engage multiple communication channels in service delivery, in order to increase the target audience and, consequently, the service effectiveness. Insofar, however, only the web channel has been sufficiently used for service delivery, whereas other channels have not been adequately exploited. One of the main reasons of this lag is the cost incurred for the development and maintenance of multiple versions of an electronic service, each version targeted to a different platform. In this paper, we present an approach and the associated tools for developing and maintaining electronic services that allows the automated production of different versions of the electronic service, each targeted to a specific platform. Β{\textcopyright} 2006 Elsevier B.V. All rights reserved.}, keywords = {Communication channels (information theory), e-government, Electronic commerce, electronic services, EServices, Government data processing, Knowledge based systems, Multi channel service delivery, Online systems, Websites}, doi = {10.1016/j.elerap.2006.07.004}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-33947371200\&partnerID=40\&md5=ebf06c2eee159fbeeab64c607e84415d}, author = {Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @conference {548, title = {MinervaDL: An Architecture for Information Retrieval and Filtering in Distributed Digital Libraries}, booktitle = {Proceedings of the 11th European Conference on Research and Advanced Technology for Digital Libraries (ECDL)}, year = {2007}, month = {September}, address = {Budapest, Hungary}, author = {Christian Zimmer and Christos Tryfonopoulos and Gerhard Weikum} } @conference {DBLP:conf/ssd/GhinitaKS07, title = {MobiHide: A Mobilea Peer-to-Peer System for Anonymous Location-Based Queries}, booktitle = {Advances in Spatial and Temporal Databases, 10th International Symposium, SSTD 2007, Boston, MA, USA, July 16-18, 2007, Proceedings}, year = {2007}, pages = {221{\textendash}238}, doi = {10.1007/978-3-540-73540-3_13}, url = {https://doi.org/10.1007/978-3-540-73540-3_13}, author = {Gabriel Ghinita and Panos Kalnis and Spiros Skiadopoulos} } @article {DBLP:journals/dke/TerrovitisVSBCMR07, title = {Modeling and language support for the management of pattern-bases}, journal = {Data Knowl. Eng.}, volume = {62}, number = {2}, year = {2007}, pages = {368{\textendash}397}, doi = {10.1016/j.datak.2006.10.002}, url = {https://doi.org/10.1016/j.datak.2006.10.002}, author = {Manolis Terrovitis and Panos Vassiliadis and Spiros Skiadopoulos and Elisa Bertino and Barbara Catania and Anna Maddalena and Stefano Rizzi} } @conference {564, title = {Node Behavior Prediction for Large-Scale Approximate Information Filtering}, booktitle = {Proceedings of the International Workshop on Large-Scale Distributed Systems for Information Retrieval (LSDS-IR @ SIGIR)}, year = {2007}, month = {July}, address = {Amsterdam, The Netherlands}, author = {Christian Zimmer and Christos Tryfonopoulos and Klaus Berberich and Gerhard Weikum and Manolis Koubarakis} } @article {Katifori2007, title = {Ontology visualization methods - A survey}, journal = {ACM Computing Surveys}, volume = {39}, number = {4}, year = {2007}, note = {cited By (since 1996) 21}, pages = {10:1-10:43}, abstract = {Ontologies, as sets of concepts and their interrelations in a specific domain, have proven to be a useful tool in the areas of digital libraries, the semantic web, and personalized information management. As a result, there is a growing need for effective ontology visualization for design, management and browsing. There exist several ontology visualization methods and also a number of techniques used in other contexts that could be adapted for ontology representation. The purpose of this article is to present these techniques and categorize their characteristics and features in order to assist method selection and promote future research in the area of ontology visualization. Β{\textcopyright} 2007 ACM.}, keywords = {Digital libraries, Human computer interaction, Information management, Ontology, Ontology representation, Ontology visualization, Personalized information management, Semantic Web, visualization methods}, doi = {10.1145/1287620.1287621}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-36048959880\&partnerID=40\&md5=a74cd76829bee9bb1cc21d6118e65340}, author = {Akrivi Katifori and C. Halatsis and Giorgos Lepouras and Costas Vassilakis and E.G. Giannopoulou} } @conference {Vasiliadis2007, title = {Performance Analysis of dual priority single-buffered blocking Multistage Interconnection Networks}, booktitle = {3rd International Conference on Networking and Services, ICNS 2007}, year = {2007}, month = {6}, publisher = {IEEE}, organization = {IEEE}, abstract = {In this paper a novel architecture of dual priority single-buffered blocking Multistage Interconnection Networks (MINs) is presented. We analyzed their performance in the uniform traffic condition under various loads using simulations. We compared the dual priority architecture against a single priority MIN, by gathering metrics for the two most important network performance factors, namely packet throughput and the mean time a packet needs to traverse the network. We demonstrated the gain of the high priority packets against the low priority packets under different configuration schemas. In this paper we focus on studying the influence of the priority bit in the header field of transmitted packets on the performance of high and low priority traffic of a MIN. Performance prediction before actual network implementation and understanding the impact of parameter settings in a MIN setup are valuable assets for network designers for minimizing overall deployment costs and delivering efficient networks. Β{\textcopyright} 2007 IEEE.}, keywords = {Computer architecture, Interconnection networks, International conferences, Low priority (LP), Metrics (CO), Multistage interconnection networks Multistage interconnection netowrk (MIN), Network architecture, Network designers, Network performances, Novel architecture, Packet throughput, Parameter estimation, Parameter settings, Performance analyses, Performance predictions, Schemas, Systems engineering, telecommunication, Telecommunication networks, Uniform traffic}, doi = {10.1109/ICNS.2007.92}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-47049115567\&partnerID=40\&md5=148ac10a4b9facdaf1066911f87f5bb5}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @conference {Vasiliadis2007a, title = {Performance evaluation of two-priority network schema for single-buffered delta networks}, booktitle = {IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC}, year = {2007}, note = {cited By (since 1996) 0}, month = {9}, abstract = {In this paper a novel two-priority network schema is presented, and exemplified through its application on singlebuffered Delta Networks in packet switching environments. Network operations considered include conflict resolution and communication strategies. The proposed scheme is evaluated and compared against the single-priority scheme. Performance evaluation was conducted through simulation, due to the complexity of the model, and uniform traffic conditions were considered. Metrics were gathered for the two most important network performance factors, namely packet throughput and the mean time a packet needs to traverse the network. The model can also be uniformly applied to several representative networks providing a basis for fair comparison and the necessary data for network designers to select optimal values for network operation parameters. Β{\textcopyright} 2007 IEEE.}, keywords = {Computer simulation, Mobile radio systems, Network operations, Packet switching, Single-buffered delta networks, Telecommunication networks, Telecommunication traffic}, doi = {10.1109/PIMRC.2007.4394153}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-44349140122\&partnerID=40\&md5=d8cd4384e09916ce753625ec5f2c8549}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis and E. Glavas} } @conference {DBLP:conf/www/GhinitaKS07, title = {PRIVE: anonymous location-based queries in distributed mobile systems}, booktitle = {Proceedings of the 16th International Conference on World Wide Web, WWW 2007, Banff, Alberta, Canada, May 8-12, 2007}, year = {2007}, pages = {371{\textendash}380}, doi = {10.1145/1242572.1242623}, url = {https://doi.org/10.1145/1242572.1242623}, author = {Gabriel Ghinita and Panos Kalnis and Spiros Skiadopoulos} } @proceedings {DBLP:conf/www/2007, title = {Proceedings of the 16th International Conference on World Wide Web, WWW 2007, Banff, Alberta, Canada, May 8-12, 2007}, year = {2007}, publisher = {ACM}, isbn = {978-1-59593-654-7}, editor = {Carey L. Williamson and Mary Ellen Zurko and Peter F. Patel-Schneider and Prashant J. Shenoy} } @proceedings {DBLP:conf/icde/2007, title = {Proceedings of the 23rd International Conference on Data Engineering, ICDE 2007, The Marmara Hotel, Istanbul, Turkey, April 15-20, 2007}, year = {2007}, publisher = {IEEE Computer Society}, isbn = {1-4244-0802-4}, url = {http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=4221634}, editor = {Rada Chirkova and Asuman Dogac and M. Tamer {\"O}zsu and Timos K. Sellis} } @conference {Vasiliadis2007937, title = {The role of priority mechanisms on performance metrics of double-buffered switching elements}, booktitle = {AIP Conference Proceedings - ICCMSE 2007}, volume = {963}, number = {2}, year = {2007}, note = {cited By (since 1996) 0}, month = {9}, pages = {937-942}, abstract = {The main concerns in designing the multistage switching fabrics are speed, throughput, delay and variance of delay for a given bandwidth. The rationale behind using various priority mechanisms is either to offer different quality of service levels to packets or to optimize performance parameters of the network, e.g. minimize internal blocking in the Switching Elements (SEs). We investigated the performance parameters of an enhanced priority (EP) mechanism versus a single priority (SP) one. In the EP scheme, packet priority was computed dynamically and was directly proportional to the transmission queue length of the SE that the packet is currently stored in. Finally, we extended the idea of the priority scheme by proposing a multi-priority (MP) mechanism. In the MP scheme, each SE has two transmission queues per link, with one queue dedicated to high priority packets and the other dedicated to low priority ones. We simulated a multistage network under the uniform traffic condition and concluded that the proposed double-buffered SEs provide higher throughput, and decreased latency. Β{\textcopyright} 2007 American Institute of Physics.}, doi = {10.1063/1.2836247}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-71449122900\&partnerID=40\&md5=3cde25f68a16c221bd7e6ac466752465}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @conference {DBLP:conf/icde/PolyzotisSVSF07, title = {Supporting Streaming Updates in an Active Data Warehouse}, booktitle = {Proceedings of the 23rd International Conference on Data Engineering, ICDE 2007, The Marmara Hotel, Istanbul, Turkey, April 15-20, 2007}, year = {2007}, pages = {476{\textendash}485}, doi = {10.1109/ICDE.2007.367893}, url = {https://doi.org/10.1109/ICDE.2007.367893}, author = {Neoklis Polyzotis and Spiros Skiadopoulos and Panos Vassiliadis and Alkis Simitsis and Nils-Erik Frantzell} } @conference {kalikakis2007a, title = {Towards a P2P world: peered taxation}, booktitle = {Proceedings of the 2nd International Workshop "E-taxation: State \& Perspectives"}, year = {2007}, month = {2}, abstract = {This paper presents the current model for taxation and distribution of the taxes to government activities, and an alternative model is presented, according to which tax-payers can determine, to some extent, the way that the taxes they pay will be spent. The goal of this proposal is to increase citizen involvment and system transparency. The model proposal comescomplete with an architecture that supports the realization of the proposed scheme}, author = {M. Kalikakis and D. Gouscos and Costas Vassilakis and P. Georgiadis} } @conference {Vassilakis20071564, title = {Web service execution streamlining}, booktitle = {Proceedings - ICSSSM{\textquoteright}06: 2006 International Conference on Service Systems and Service Management}, volume = {2}, year = {2007}, note = {cited By (since 1996) 0}, month = {10}, pages = {1564-1569}, abstract = {Web services are functional, independent components that can be called over the web to perform a task. Besides being used individually to deliver some well-specified functionality, web services may be used as building blocks that can be combined to implement a more complex function. In such compositions, typically some web services produce results that are used as input for web services that will be subsequently invoked. In the execution schemes currently employed, web services producing intermediate results deliver them to some "coordinating entity", which arranges the forwarding of these intermediate results to web services that require them as input. In this paper we present an execution scheme that employs direct communication between producers and consumers of intermediate results. Besides performance improvement stemming from reduction of network communication, this scheme permits consumer web services to employ simpler authenticity and integrity verification algorithms on incoming parameters. when the producer web service is considered trustworthy. Β{\textcopyright}2006 IEEE.}, keywords = {Algorithms, Function evaluation, Optimization, Parameter estimation, Streamlining, Web service execution, Web service synthesis, Web services}, doi = {10.1109/ICSSSM.2006.320769}, url = {http://ieeexplore.ieee.org/document/4114724/}, author = {Costas Vassilakis and Giorgos Lepouras and Akrivi Katifori} } @conference {1154709, title = {A Comparative Study of Four Ontology Visualization Techniques in Protege: Experiment Setup and Preliminary Results}, booktitle = {IV {\textquoteright}06: Proceedings of the conference on Information Visualization}, year = {2006}, month = {7}, pages = {417{\textendash}423}, publisher = {IEEE Computer Society}, organization = {IEEE Computer Society}, address = {Washington, DC, USA}, abstract = {The continuing need for more effective information retrieval has lead to the creation of the notions of the semantic web and personalized information management, areas of study that very often employ ontologies to represent the semantic context of a domain. Consequently, the need for effective ontology visualization for design, management and browsing has arisen. There are several ontology visualizations available through the existing ontology management tools, but not as many evaluations to determine their advantages and disadvantages and their suitability for various ontologies and user groups. This work presents the preliminary results of an evaluation of four visualization methods in Protege.}, isbn = {0-7695-2602-0}, doi = {10.1109/IV.2006.3}, author = {Akrivi Katifori and Elena Torou and C. Halatsis and Giorgos Lepouras and Costas Vassilakis} } @article {1412314, title = {Component reuse in electronic services development}, journal = {J. Comp. Methods in Sci. and Eng.}, volume = {6}, number = {5,6 Supplement 2}, year = {2006}, pages = {229{\textendash}241}, publisher = {IOS Press}, address = {Amsterdam, The Netherlands, The Netherlands}, abstract = {In the context of electronic government, e-services are a valuable instrument for offering high quality services to enterprises and individual citizens alike. While developing an e-service, it is usually possible to reuse elements that have already crafted for other e-services, such as personal detail forms or widgets for collecting social security numbers, decreasing thus both development effort and the time for deployment. A more generic framework for supporting reusability in development of e-services includes the identification of reusable objects, the creation and population of a repository containing such components, and the empowerment of developers with tools allowing for location, retrieval and adaptation of components for suiting their specific tasks. In this paper, we conduct an analysis to recognise e-service component that offer reusability opportunities and we present facilities and methods to enable e-service developers to exploit these opportunities while developing electronic services.}, issn = {1472-7978}, url = {http://content.iospress.com/articles/journal-of-computational-methods-in-sciences-and-engineering/jcm00134}, author = {Costas Vassilakis and Giorgos Lepouras} } @conference {Golemati200662, title = {A context-based adaptive visualization environment}, booktitle = {Proceedings of the International Conference on Information Visualisation}, year = {2006}, note = {cited By (since 1996) 0}, month = {7}, pages = {62-67}, abstract = {Digital libraries and historical archives are increasingly employing visualization systems to facilitate the information retrieval and knowledge extraction tasks of their users. Typically, each organization employs a single visualization system, which may not suit best the needs of certain user groups, specific tasks, or properties of document collections to be visualized. In this paper we present a context-based adaptive visualization environment, which embeds a set of visualization methods into a visualization library, from which the most appropriate one is selected for presenting information to the user. Methods are selected by examining parameters related to the user profile, system configuration and the set of data to be visualized, and employing a set of rules to assess the suitability of each method. The presented environment additionally monitors user behavior and preferences to adapt the visualization method selection criteria. Β{\textcopyright} 2006 IEEE.}, keywords = {(PL) properties, Adaptive systems, Adaptive visualization, Behavioral research, Digital libraries, document collections, Extraction, Information analysis, Information science, Information services, Information systems, Information visualization, Knowledge extraction, Libraries, Retrieval (MIR), Search engines, Selection criterion, Set of rules, Solvent extraction, Specific tasks, System configurations, User behaviors, User groups, user profiling, Visualization, visualization methods, Visualization systems}, doi = {10.1109/IV.2006.5}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-45149121827\&partnerID=40\&md5=ec45ad555b132faaf0bd2ca53e3292dc}, author = {M. Golemati and C. Halatsis and Costas Vassilakis and Akrivi Katifori and Giorgos Lepouras} } @conference {DBLP:conf/icdim/TorouKVLH06, title = {Creating an Historical Archive Ontology: Guidelines and Evaluation}, booktitle = {ICDIM}, year = {2006}, month = {12}, pages = {102-109}, abstract = {Ontologies have been proven invaluable tools both for the semantic web and for personal information management. In the context of a historical archive an ontology may provide meaningful and efficient support for search tasks as well as be used as a tool for storage and presentation of historical data. The creation however of such an ontology is complex, since the digitized archive documents are not in text format and the concepts that must be captured may vary among different time periods. This work presents a user-centric methodological approach for extracting the ontology of an historical archive focusing on the evaluation issues related to this process. The approach is exemplified through cases from its application in the University of Athens Historical Archive.}, doi = {10.1109/ICDIM.2007.369337}, author = {Elena Torou and Akrivi Katifori and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @conference {597, title = {Design and Evaluation of Semantic Similarity Measures for Concepts Stemming from the Same or Different Ontologies}, booktitle = {Proceedings of the 4th Workshop on Multimedia Semantics (WMS)}, year = {2006}, month = {June}, address = {Chania, Crete, Greece}, abstract = {Semantic Similarity relates to computing the similarity between concepts (terms) which are not necessarily lexically similar. We investigate approaches to computing semantic similarity by mapping terms to an ontology and by examining their relationships in that ontology. More specifically, we investigate approaches to computing the semantic similarity between natural language terms (using WordNet as the underlying reference ontology) and between medical terms (using the MeSH ontology of medical and biomedical terms). The most popular semantic similarity methods are implemented and evaluated using WordNet and MeSH. The focus of this work is also on cross ontology methods which are capable of computing the semantic similarity between terms stemming from different ontologies (WordNet and MeSH in this work). This is a far more difficult problem (than the single ontology one referred to above) which has not been investigated adequately in the literature. X-Similarity, a novel cross-ontology similarity method is also a contribution of this work. All methods examined in this work are integrated into a semantic similarity system which is accessible on the Web.}, author = {E.G.M. Petrakis and Giannis Varelas and Angelos Hliaoutakis and Paraskevi Raftopoulou} } @conference {559, title = {Distributed Evaluation of Continuous Equi-join Queries over Large Structured Overlay Networks}, booktitle = {Proceedings of the 22nd International Conference on Data Engineering (ICDE)}, year = {2006}, month = {April}, address = {Atlanda, USA}, author = {Stratos Idreos and Christos Tryfonopoulos and Manolis Koubarakis} } @inbook {vas2006a, title = {Encyclopedia of E-Commerce, E-Government and Mobile Commerce}, year = {2006}, pages = {865{\textendash}870}, publisher = {Idea Group Inc.}, organization = {Idea Group Inc.}, chapter = {Ontology for e-Government public services}, abstract = {In this work, the usage of ontologies for meeting requirements related to e-service composition, e-service cataloguing, change management and administrative responsibility is examined. An ontology for e-government services is presented, covering various aspects of services, including administrative responsibility, meta-data, involved documents and legislation. Both the development and usage phase of the ontology are covered and directions for further exploitation of the potential offered by the ontological representation are given.}, doi = {10.4018/978-1-59140-799-7.ch139}, author = {Costas Vassilakis and Giorgos Lepouras}, editor = {Mehdi Khosrow-Pour} } @inbook {lep2006b, title = {Encyclopedia of E-Commerce, E-Government and Mobile Commerce}, year = {2006}, pages = {1{\textendash}6}, publisher = {Idea Group Inc.}, organization = {Idea Group Inc.}, chapter = {Adaptive Virtual Reality Shopping Malls}, abstract = {Firms and organizations are increasingly exploiting electronic channels to reach their customers and create new business opportunities. To this end, electronic shops have been developed, either offering products from a single firm or encompassing multiple individual electronic stores, comprising thus electronic shopping malls. Two main concerns for e-commerce are personalization and enhancement of user experience. Personalization addresses the ability to offer content tailored to the preferences of each user or user group. Preferences may be explicitly declared by the user, or derived by the system through inspecting user interaction; if the system dynamically reacts to changes of visitor behavior, it is termed as adaptive. Enhancement of user experience is another major issue in e-commerce, given that 2D-images and texts on the screen are not sufficient to provide information on products aspects such as physical dimensions, textures and manipulation feedback. Multimedia presentations can also be used as a means for .information acceleration. for promoting "really new" products. This article aims to specify a system that exploits capabilities offered by adaptation and VR technologies to offer e-shoppers personalized and enhanced experiences, while addressing challenges related to the cost, complexity and effort of building and maintaining such a system.}, doi = {10.4018/978-1-59904-955-7.ch099}, author = {Giorgos Lepouras and Costas Vassilakis}, editor = {Mehdi Khosrow-Pour} } @inbook {lep2006a, title = {Encyclopedia of E-Commerce, E-Government and Mobile Commerce}, year = {2006}, pages = {1064{\textendash}1069}, publisher = {Idea Group Inc.}, organization = {Idea Group Inc.}, chapter = {Tailorable e-government information systems}, abstract = {Real-world information, knowledge and procedures after which information systems are modeled are generally of dynamic nature and subject to changes, due to the emergence of new requirements or revisions to initial specifications. E-government information systems (eGIS) present a higher degree of volatility in their environment, since requirement changes may stem from multiple sources, including legislation changes, organizational reforms, end-user needs, interoperability and distribution concerns etc. To this end, the design and implementation of eGIS must adhere to paradigms and practices that facilitate the accommodation of changes to the eGIS as they occur in the real world. In this work, we present a role-based model for designing and implementing eGIS that can dynamically accomodate changes, providing the necessary facilities for modeling multiple aspects of the same real-world entities and delivering context-specific behaviour.}, doi = {10.4018/978-1-59140-799-7.ch171}, author = {Giorgos Lepouras and Anya Sotiropoulou and Dimitrios Theotokis and Costas Vassilakis}, editor = {Mehdi Khosrow-Pour} } @article {DBLP:journals/tkde/KoubarakisST06, title = {Logic and Computational Complexity for Boolean Information Retrieval}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {18}, number = {12}, year = {2006}, pages = {1659{\textendash}1666}, doi = {10.1109/TKDE.2006.193}, url = {https://doi.org/10.1109/TKDE.2006.193}, author = {Manolis Koubarakis and Spiros Skiadopoulos and Christos Tryfonopoulos} } @conference {adpuc06-BKTWZ, title = {MAPS: Approximate Publish/Subscribe Functionality in Peer-to-Peer Networks}, booktitle = {Proceedings of Advanced Data Processing in Ubiquitous Computing Workshop (ADPUC @ Middleware)}, year = {2006}, month = {November}, pages = {1{\textendash}6}, address = {Melbourne, Australia}, author = {Klaus Berberich and Manolis Koubarakis and Christos Tryfonopoulos and Gerhard Weikum and Christian Zimmer} } @conference {Vasiliadis2006b, title = {Performance analysis of blocking banyan switches}, booktitle = {Proceedings of the IEEE sponsored International Joint Conference on Computer, Information and System Sciences and Engineering - CIS2E 06}, year = {2006}, month = {12}, abstract = {Banyan Networks are a major class of Multistage Interconnection Networks (MINs). They have been widely used as efficient interconnection structures for parallel computer systems, as well as switching nodes for high-speed communication networks. The performance of them is mainly determined by their communication throughput and their mean packet delay. In this paper we use a model that is based on a universal performance factor, which includes the importance aspect of each of the above main performance factors (throughput and delay) in the design process of a MIN. The model can also uniformly be applied to several representative networks. The complexity of the model requires to be investigated by time-consuming simulations. In this paper we study a typical (8X8) Baseline Banyan Switch that consists of (2X2) Switching Elements (SEs). The objective of this simulation is to determine the optimal buffer size for the MIN stages under different conditions.}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @conference {Vasiliadis2006a, title = {Performance Analysis of Multistage Interconnection Networks determining optimal parameters for data-intensive business applications}, booktitle = {Proceedings of the 7th IBIMA Conference}, year = {2006}, month = {12}, abstract = {Multistage Interconnection Networks (MINs) are frequently used for connecting processors in parallel computing systems or constructing high speed networks such as ATM (based on Asynchronous Transfer Mode) and Gigabit Ethernet Switches. New applications require distributed computing implementations, but old networks are too slow to allow efficient use of remote resources. Moreover, multimedia are considered as applications with high bandwidth requirements. Some of them are also sensitive to packet loss and claim reliable data transmission. Specific applications require bulk data transfers for database replication or load balancing and therefore packet loss minimization is necessary in order to increase the performance of them. The demand for high performance multimedia services such as full motion video on demand is becoming an increasingly important driving force in the communication market in the Digital Age. Thus, the performance of MINs is a crucial factor, which we have to take into account in the design of new applications. Their performance is mainly determined by their communication throughput and cell latency, which have to be investigated either by time-consuming simulations or approximated by mathematical models. In this paper we investigate the performance of MINs in order to determine optimal values for hardware parameters under diferent operating conditions.}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis} } @conference {DBLP:conf/icsoft/VassilakisLK06, title = {Reverse engineering electronic services: from e-forms to knowledge}, booktitle = {ICSOFT (1)}, year = {2006}, month = {9}, pages = {273-278}, abstract = {On their route to e-governance, public administrations have developed e-services. Each e-service encompasses a significant amount of knowledge in the form of examples, help texts, legislation excerpts, validation checks etc. This knowledge has been offered by domain experts in the phases of service analysis, design and implementation, being however bundled within the software, it cannot be readily retrieved and used in other organizational processes, including the development of new services. In this paper, we present an approach for reverse engineering e-services, in order to formulate knowledge items of a high level of abstraction, which can be made available to the employees of the organizations. Moreover, the knowledge items formulated in the reverse engineering process are stored into a knowledge-based e-service development platform, making them readily available for use in the development of other services.}, author = {Costas Vassilakis and Giorgos Lepouras and Akrivi Katifori} } @conference {kareliotis2006, title = {Towards Dynamic, Relevance-Driven Exception Resolution in Composite Web Services}, booktitle = {Proceedings of OOPSLA 2006, Fourth International Workshop on SOA \& Web Services Best Practices}, year = {2006}, month = {10}, abstract = {Web services have become the leading technology for application-toapplication (A2A) communication over distributed and heterogeneous environments. Both academia and industry have strived to enable useful service collaborations among distributed systems without any human intervention. Web service composition can be used to this end, to achieve business automation within one company or realize business-to-business (B2B) integration of heterogeneous software and cross-organizational computing systems. Service composition pro-vides added value, when a web service composition itself becomes a higher level composite web service. However, as business processes are long-lasting transactions, exceptions may often occur, necessitating the replacement of a service component which has been made unavailable, hindering the completion of some business process. In this paper we present an exception resolving approach based on discovering replacement components that are functionally equivalent, taking also into account criteria for qualitative substitutability. The proposed solution introduces the Service Relevance and Replacement Framework (SRRF) which undertakes exception handling.}, author = {Christos Kareliotis and Costas Vassilakis and P. Georgiadis} } @article {Magoulas200771, title = {Virtual reality in the e-Society}, journal = {Virtual Reality}, volume = {11}, number = {2-3}, year = {2006}, note = {cited By (since 1996) 1}, month = {dec}, pages = {71-73}, publisher = {Springer Nature}, abstract = {This special issue explores the extent to which virtual reality (VR) is affecting the creation of an electronic society. E-Society is a broad term used to describe a research area covering aspects of digital technologies for large user communities. Recent years have seen the emergence of various electronic services in an attempt to facilitate everyday life and improve the way common tasks are being carried out. The term e-Society covers a wide range of applications from e-government, e-democracy, and e-business to e-learning and e-health. In order for VR to contribute to the creation and advancement of e-Society, a number of issues have to be tackled. A successful VR system has to find a balance between the hardware requirements, user interaction methods, content presentation and the effort required for development and maintenance. Hardware requirements define to a large degree the extent to which an end-user can afford to execute the VR system at her home. User interaction methods have to cater for the variety of users? needs. Overall, design and implementation of a successful and engaging VR system is a rather difficult and complex task which requires increased effort in human power and resources in comparison to typical window based applications. Flexibility in development and subsequently maintenance of such a system can be achieved by adopting techniques already present in rapid application development environments, like abstraction, automatic code generation and reusability.}, doi = {10.1007/s10055-006-0064-0}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-34347395236\&partnerID=40\&md5=88157a2c66f3799e7bcfaf75eda9548a}, author = {G. D. Magoulas and Giorgos Lepouras and Costas Vassilakis} } @conference {1133365, title = {Visualizing a temporally-enhanced ontology}, booktitle = {AVI {\textquoteright}06: Proceedings of the working conference on Advanced visual interfaces}, year = {2006}, month = {5}, pages = {488{\textendash}491}, publisher = {ACM}, organization = {ACM}, address = {New York, NY, USA}, abstract = {Most ontology development methodologies and tools for ontology management deal with ontology snapshots, i.e. they model and manage only the most recent version of ontologies, which is inadequate for contexts where the history of the ontology is of interest, such as historical archives. This work presents a modeling for entity and relationship timelines in the Prot.g. tool, complemented with a visualization plug-in, which enables users to examine entity evolution along the timeline.}, isbn = {1-59593-353-0}, doi = {10.1145/1133265.1133365}, author = {Akrivi Katifori and Costas Vassilakis and Giorgos Lepouras and I. Daradimos and C. Halatsis} } @article {592, title = {X-Similarity: Computing Semantic Similarity between Concepts from Different Ontologies}, journal = {Journal of Digital Information Management (JDIM)}, year = {2006}, month = {December}, abstract = {Semantic Similarity relates to computing the similarity between concepts (terms) which are not necessarily lexically similar. We investigate approaches to computing semantic similarity by mapping terms to an ontology and by examining their relationships in that ontology. More specifically, we investigate approaches to computing the semantic similarity between natural language terms (using WordNet as the underlying reference ontology) and between medical terms (using the MeSH ontology of medical and biomedical terms). The most popular semantic similarity methods are implemented and evaluated using WordNet and MeSH. The focus of this work is also on cross ontology methods which are capable of computing the semantic similarity between terms stemming from different ontologies (WordNet and MeSH in this work). This is a far more difficult problem (than the single ontology one referred to above) which has not been investigated adequately in the literature. X-Similarity, a novel cross-ontology similarity method is also a contribution of this work. All methods examined in this work are integrated into a semantic similarity system which is accessible on the Web.}, author = {E.G.M. Petrakis and Giannis Varelas and Angelos Hliaoutakis and Paraskevi Raftopoulou} } @conference {Lepouras2005573, title = {An active ontology-based blackboard architecture for Web service interoperability}, booktitle = {2005 International Conference on Services Systems and Services Management, Proceedings of ICSSSM{\textquoteright}05}, volume = {1}, year = {2005}, note = {cited By (since 1996) 1}, month = {6}, pages = {573-578}, abstract = {Web services are functional, independent components that can be called over the web to perform a task. Web services are provided by organizations to enable others to perform tasks the organization offers online. However, with an ever increasing number of web services, finding the web service that performs a certain task is not always easy. Furthermore, adopting an end-user point of view what is needed is the actual result and not the service per se. It is often the case that more than one service have to be combined to produce the anticipated outcome, e.g. in the case of life-events. To this end, we propose an active, ontology-based blackboard architecture that aims at tackling the problems inherent in dynamic synthesis of composite web services and at facilitating user interaction with complex e-government transactions. Β{\textcopyright} 2005 IEEE.}, keywords = {Active blackboard architecture, Computer architecture, Electronic commerce, Interoperability, Ontology-based architecture, Web service synthesis, World Wide Web}, doi = {10.1109/ICSSSM.2005.1499537}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-33745256434\&partnerID=40\&md5=d1cd6446d2f3bc9ed098036d2f2bd384}, author = {Giorgos Lepouras and Costas Vassilakis and Anya Sotiropoulou and Dimitrios Theotokis and Akrivi Katifori} } @inbook {lepbook2005a, title = {Adaptable and Adaptive Hypermedia Systems}, year = {2005}, pages = {190{\textendash}205}, publisher = {IRM Press}, organization = {IRM Press}, chapter = {Adaptive Virtual Museums on the Web}, abstract = {This chapter presents an architecture for supporting the creation of adaptive virtual reality museums on the web. It argues whether the task of developing adaptive virtual reality museums is a complex one, presenting key challenges, and should thus be facilitated by means of a supporting architecture and relevant tools. The proposed architecture is flexible enough to cater for a variety of user needs, and modular promoting extensibility, maintainability and tailorability. Adoption of this architecture will greatly simplify the development of adaptive virtual reality museums, reducing the needed effort to exhibit digitisation and user profile specification; user profiles are further refined dynamically through the user data recorder and the user modelling engine, which provide input for the virtual environment generator.}, doi = {10.4018/978-1-59140-567-2.ch010}, author = {Giorgos Lepouras and Costas Vassilakis}, editor = {S. Y. Chen and G. D. Magoulas} } @article {Vassilakis_barriersto, title = {Barriers To Electronic Service Development}, journal = {e-Service Journal}, volume = {Fall 2005}, year = {2005}, pages = {41-63}, abstract = {E-government initiatives have been proven to deliver significant benefits, both for suppliers of electronic services (public authorities and organizations) and for the public, to whom services are addressed. However, the pace with which electronic services are made available and adopted is lower than planned or expected; governments tend to be slow in releasing new services, and citizens often prefer to conduct business with the government through paper forms and physical presence, rather than using online methods. This indicates that certain barriers exist that hinder the transition to electronic services. In this paper, we present the results of a survey among electronic service stakeholder groups, to identify the most important barriers to electronic service development. Documentation of barriers is considered important, since administrations may take certain measures to overcome them. Hints on how specific barriers may be overcome are also provided.}, doi = {10.2979/esj.2005.4.1.41}, author = {Costas Vassilakis and Giorgos Lepouras and John Fraser and Simon Haston} } @conference {vassilakis05b, title = {A Blackboard-oriented Architecture for e-Government service composition}, booktitle = {Proceedings of the IRMA 2005 conference}, year = {2005}, month = {5}, abstract = {A requirement for electronic government initiatives to succeed is the ability to offer a citizen-centric view of the government model. The most widely adopted paradigm supporting this task is the life event model, which combines basic services offered from multiple public authorities into a single, high-level service that corresponds to an event in a citizen{\textquoteright}s life. This composition is not always straightforward though, because the constituent services are generally developed in an independent fashion, using incompatible input and output formats; moreover the task of synchronising the documents required and produced by the services is tedious to implement and costly to maintain, since changes to requirements and legislation necessitate continuous updates to this scheme. In this paper, we present a blackboard architecture that can be used to deliver life-event oriented services to the citizens. The blackboard proposed for this architecture is an active one, undertaking the tasks of conversions, where appropriate. The blackboard couples a data flow approach with event-condition-action rules to enable dynamic formulation of life-event services, decentralising their development and maintenance.}, author = {Costas Vassilakis and Anya Sotiropoulou and Dimitrios Theotokis and D. Gouscos} } @conference {DBLP:conf/er/VassiliadisSTS05, title = {Blueprints and Measures for ETL Workflows}, booktitle = {Conceptual Modeling - ER 2005, 24th International Conference on Conceptual Modeling, Klagenfurt, Austria, October 24-28, 2005, Proceedings}, year = {2005}, pages = {385{\textendash}400}, doi = {10.1007/11568322_25}, url = {https://doi.org/10.1007/11568322_25}, author = {Panos Vassiliadis and Alkis Simitsis and Manolis Terrovitis and Spiros Skiadopoulos} } @article {DBLP:journals/tkde/SkiadopoulosGSVSK05, title = {Computing and Managing Cardinal Direction Relations}, journal = {IEEE Trans. Knowl. Data Eng.}, volume = {17}, number = {12}, year = {2005}, pages = {1610{\textendash}1623}, doi = {10.1109/TKDE.2005.192}, url = {https://doi.org/10.1109/TKDE.2005.192}, author = {Spiros Skiadopoulos and Christos Giannoukos and Nikos Sarkas and Panos Vassiliadis and Timos K. Sellis and Manolis Koubarakis} } @proceedings {DBLP:conf/er/2005, title = {Conceptual Modeling - ER 2005, 24th International Conference on Conceptual Modeling, Klagenfurt, Austria, October 24-28, 2005, Proceedings}, volume = {3716}, year = {2005}, publisher = {Springer}, isbn = {3-540-29389-2}, doi = {10.1007/11568322}, url = {https://doi.org/10.1007/11568322}, editor = {Lois M. L. Delcambre and Christian Kop and Heinrich C. Mayr and John Mylopoulos and Oscar Pastor} } @article {DBLP:journals/ai/SkiadopoulosK05, title = {On the consistency of cardinal direction constraints}, journal = {Artif. Intell.}, volume = {163}, number = {1}, year = {2005}, pages = {91{\textendash}135}, doi = {10.1016/j.artint.2004.10.010}, url = {https://doi.org/10.1016/j.artint.2004.10.010}, author = {Spiros Skiadopoulos and Manolis Koubarakis} } @proceedings {DBLP:conf/dawak/2005, title = {Data Warehousing and Knowledge Discovery, 7th International Conference, DaWaK 2005, Copenhagen, Denmark, August 22-26, 2005, Proceedings}, volume = {3589}, year = {2005}, publisher = {Springer}, isbn = {3-540-28558-X}, doi = {10.1007/11546849}, url = {https://doi.org/10.1007/11546849}, editor = {A Min Tjoa and Juan Trujillo} } @article {Vassilakis200581, title = {Exploiting form semantics and validation checks to improve e-form layout}, journal = {International Journal of Web Engineering and Technology}, volume = {2}, number = {1}, year = {2005}, note = {cited By (since 1996) 0}, pages = {81-96}, abstract = {On their route to the electronic era, organisations release on the web more and more complex form-based services, which require users to enter numerous data items interrelated by business rules. In such a context, it is crucial to provide optimal form layouts, in order to present the service users with interfaces that facilitate their work. This paper presents an integrated environment, which exploits data item interrelations manifested by the business rules (or validation checks), to optimise the layout of the web forms comprising a complex service. The approach is validated through its application on a tax return form e-service. Copyright Β{\textcopyright} 2005 Inderscience Enterprises Ltd.}, keywords = {electronic services, Form layout, Form semantics, Integrated environment, Interfaces (computer), Optimization, semantics, Taxation, Usuability, Validation checks, World Wide Web}, doi = {10.1504/IJWET.2005.007465}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-24344507764\&partnerID=40\&md5=e94b487785303410cb7bf88df9d12c86}, author = {Costas Vassilakis and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @article {593, title = {Fair Resource Allocation in a Simple Multi-Agent Setting: Search Algorithms and Experimental Evaluation}, journal = {International Journal on Artificial Intelligence Tools (IJAIT)}, volume = {14}, year = {2005}, month = {December}, pages = {887{\textendash}899}, abstract = {We study the problem of fair resource allocation in a simple cooperative multi-agent setting where we have k agents and a set of n objects to be allocated to those agents. Each object is associated with a weight represented by a positive integer or real number. We would like to allocate all objects to the agents so that each object is allocated to only one agent and the weight is distributed fairly. We adopt the fairness index popularized by the networking community as our measure of fairness, and study centralized algorithms for fair resource allocation. Based on the relationship between our problem and number partitioning, we devise a greedy algorithm for fair resource allocation that runs in polynomial time but is not guaranteed to find the optimal solution, and a complete anytime algorithm that finds the optimal solution but runs in exponential time. Then we study the phase transition behavior of the complete algorithm. Finally, we demonstrate that the greedy algorithm actually performs very well and returns almost perfectly fair allocations.}, keywords = {Fairness; resource allocation; number partitioning; phase transitions}, author = {Paraskevi Raftopoulou and Manolis Koubarakis and Kostas Stergiou and Peter Triantafillou} } @article {Souillard2005453, title = {A flexible framework for managing temporal clinical trial data}, journal = {International Journal of Electronic Healthcare}, volume = {1}, number = {4}, year = {2005}, note = {cited By (since 1996) 2}, pages = {453-463}, abstract = {Clinical trials are processes that produce large volumes of complex data, with inherent temporal requirements, since the state of patients evolves during the trials, and the data acquisition phase itself needs to be monitored. Additionally, since the requirements for all clinical trials have a significant common portion, it is desirable to capture these common requirements in a generalised framework, which will be instantiated for each specific trial by supplementing the trial-specific requirements. In this paper, we present an integral approach to clinical trial management, using a temporal object-oriented methodology to capture and model the requirements, a temporal OODBMS for data storage and a generalised template application, through which trial-specific applications may be generated. Copyright Β{\textcopyright} 2005 Inderscience Enterprises Ltd.}, keywords = {data base, information processing, medical information system, medical research, patient information, Quality control, review, telecommunication}, doi = {10.1504/IJEH.2005.006691}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-21244469415\&partnerID=40\&md5=10bcf05c2826591c7ee952d0b3eecb1b}, author = {Michael Souillard and Souveyet, C. and Costas Vassilakis and Anya Sotiropoulou} } @article {DBLP:journals/is/VassiliadisSGTS05, title = {A generic and customizable framework for the design of ETL scenarios}, journal = {Inf. Syst.}, volume = {30}, number = {7}, year = {2005}, pages = {492{\textendash}525}, doi = {10.1016/j.is.2004.11.002}, url = {https://doi.org/10.1016/j.is.2004.11.002}, author = {Panos Vassiliadis and Alkis Simitsis and Panos Georgantas and Manolis Terrovitis and Spiros Skiadopoulos} } @conference {DBLP:conf/dawak/SimitsisVTS05, title = {Graph-Based Modeling of ETL Activities with Multi-level Transformations and Updates}, booktitle = {Data Warehousing and Knowledge Discovery, 7th International Conference, DaWaK 2005, Copenhagen, Denmark, August 22-26, 2005, Proceedings}, year = {2005}, pages = {43{\textendash}52}, doi = {10.1007/11546849_5}, url = {https://doi.org/10.1007/11546849_5}, author = {Alkis Simitsis and Panos Vassiliadis and Manolis Terrovitis and Spiros Skiadopoulos} } @conference {547, title = {LibraRing: An Architecture for Distributed Digital Libraries Based on DHTs}, booktitle = {Proceedings of the 9th European Conference on Research and Advanced Technology for Digital Libraries (ECDL)}, year = {2005}, month = {September}, address = {Vienna, Austria}, author = {Christos Tryfonopoulos and Stratos Idreos and Manolis Koubarakis} } @article {DBLP:journals/jdwm/ManiatisVSVMM05, title = {A Presentation Model \& Non-Traditional Visualization for OLAP}, journal = {IJDWM}, volume = {1}, number = {1}, year = {2005}, pages = {1{\textendash}36}, doi = {10.4018/jdwm.2005010101}, url = {https://doi.org/10.4018/jdwm.2005010101}, author = {Andreas S. Maniatis and Panos Vassiliadis and Spiros Skiadopoulos and Yannis Vassiliou and George Mavrogonatos and Ilias Michalarias} } @conference {542, title = {Publish/Subscribe Functionalities for Future Digital Libraries using Structured Overlay Networks}, booktitle = {Proceedings of the 8th International Workshop of the DELOS Network of Excellence on Digital Libraries on Future Digital Library Management Systems}, year = {2005}, month = {March}, address = {Schloss Dagstuhl, Germany}, author = {Christos Tryfonopoulos and Stratos Idreos and Manolis Koubarakis} } @conference {573, title = {Publish/Subscribe Functionality in IR Environments using Structured Overlay Networks}, booktitle = {Proceedings of the 28th Annual International ACM SIGIR Conference}, year = {2005}, month = {August}, address = {Salvador, Brazil}, author = {Christos Tryfonopoulos and Stratos Idreos and Manolis Koubarakis} } @conference {598, title = {Semantic Similarity Methods in WordNet and their Application to Information Retrieval on the Web}, booktitle = {Proceedings of 7th ACM International Workshop on Web Information and Data Management (WIDM)}, year = {2005}, month = {November}, publisher = {ACM}, organization = {ACM}, address = {Bremen, Germany}, abstract = {Semantic Similarity relates to computing the similarity be- tween concepts which are not lexicographically similar. We investigate approaches to computing semantic similarity by mapping terms (concepts) to an ontology and by examining their relationships in that ontology. Some of the most popular semantic similarity methods are implemented and evaluated using WordNet as the underlying reference ontology. Building upon the idea of semantic similarity, a novel information retrieval method is also proposed. This method is capable of detecting similarities between documents containing semantically similar but not necessarily lexicographically similar terms. The proposed method has been evaluated in retrieval of images and documents on the Web. The experimental results demonstrated very promising performance improvements over state-of-the-art information retrieval methods.}, keywords = {Information retrieval, Semantic Similarity, WordNet, World Wide Web}, author = {Giannis Varelas and Epimenides Voutsakis and Paraskevi Raftopoulou and E.G.M. Petrakis and Evangelos Milios} } @conference {Vassilakis2005421, title = {A semantics-based consultations workbench}, booktitle = {ITI 3rd International Conference on Information and Communications Technology, ICICT 2005 - Enabling Technologies for the New Knowledge Society}, volume = {2005}, year = {2005}, note = {cited By (since 1996) 0}, month = {12}, pages = {421-434}, abstract = {Econsultations constitute an effective means to inclusive and informed participation of citizens and society in policy, decision and law formulation processes, and an answer to democratic deficit issues. Econsultation platforms need to support all stages of consultation processes including agenda setting and topics raising, legislation proposal publicity, notification of developments, proposal debate and commentary, collection, analysis and synthesis of views. In this paper we present the design of an open platform assisting policy makers and the civil society in the set-up, enactment, management and federation of inclusive and informed digital consultations. The proposed platform employs semantic techniques, such as semantics, content annotation and summarization to support the consultation processes and provide targeted and digested information to participants, and facilitates tailoring of Econsultation procedures by offering basic Econsultation activities as building blocks, which can be combined according to contextual needs. The platform also enables distinct Econsultation processes to be federated, allowing the exchange of information, which may be subject to different semantic annotations and classifications, according to the rules of each Econsultation process.}, keywords = {Classification (of information), Content annotation, Data transfer, Decision making, Econsultations, Knowledge based systems, Logic programming, Platform architecture, Public policy, Semantic technologies, semantics}, doi = {10.1109/ITICT.2005.1609641}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-33847729948\&partnerID=40\&md5=54c7a246c0ee9ae483889741a327253b}, author = {Costas Vassilakis and D. Gouscos and P. Georgiadis} } @article {DBLP:journals/eg/VassilakisLHL05, title = {An XML model for electronic services}, journal = {Electronic Government}, volume = {2}, number = {1}, year = {2005}, pages = {41-55}, abstract = {With the need for electronic services to be developed and deployed more and more rapidly, it is imperative that concrete models of electronic services are developed, to facilitate systematic work of electronic service stakeholders, concrete semantics and coherent representations across services developed within an organisation. Using the XML language to develop such a model, offers a number of additional advantages, such as rich semantics, facilitation of data interchange, extensibility, high abstraction levels and possibility for mechanical processing. In this paper we present the design aspects of an XML model for electronic services, which has been used for building a repository of interlinked elements representing e-services. A web-based interface for the management of this repository and a tool for automatically compiling e-service descriptions into executable images have been developed alongside. The model has been evaluated by a mixture of electronic service stakeholders, and the results of this evaluation are also presented.}, doi = {10.1504/EG.2005.006647}, author = {Costas Vassilakis and Giorgos Lepouras and C. Halatsis and Tomas Pariente Lobo} } @proceedings {DBLP:conf/edbt/2004, title = {Advances in Database Technology - EDBT 2004, 9th International Conference on Extending Database Technology, Heraklion, Crete, Greece, March 14-18, 2004, Proceedings}, volume = {2992}, year = {2004}, publisher = {Springer}, isbn = {3-540-21200-0}, doi = {10.1007/b95855}, url = {https://doi.org/10.1007/b95855}, editor = {Elisa Bertino and Stavros Christodoulakis and Dimitris Plexousakis and Vassilis Christophides and Manolis Koubarakis and Klemens B{\"o}hm and Elena Ferrari} } @article {DBLP:journals/ai/SkiadopoulosK04, title = {Composing cardinal direction relations}, journal = {Artif. Intell.}, volume = {152}, number = {2}, year = {2004}, pages = {143{\textendash}171}, doi = {10.1016/S0004-3702(03)00137-1}, url = {https://doi.org/10.1016/S0004-3702(03)00137-1}, author = {Spiros Skiadopoulos and Manolis Koubarakis} } @conference {DBLP:conf/edbt/SkiadopoulosGVSK04, title = {Computing and Handling Cardinal Direction Information}, booktitle = {Advances in Database Technology - EDBT 2004, 9th International Conference on Extending Database Technology, Heraklion, Crete, Greece, March 14-18, 2004, Proceedings}, year = {2004}, pages = {329{\textendash}347}, doi = {10.1007/978-3-540-24741-8_20}, url = {https://doi.org/10.1007/978-3-540-24741-8_20}, author = {Spiros Skiadopoulos and Christos Giannoukos and Panos Vassiliadis and Timos K. Sellis and Manolis Koubarakis} } @conference {Weir2004152, title = {Content enrichment through dynamic annotation}, booktitle = {ICEIS 2004 - Proceedings of the Sixth International Conference on Enterprise Information Systems}, year = {2004}, note = {cited By (since 1996) 0}, month = {4}, pages = {152-157}, abstract = {This paper describes a technique for interceding between users and the information that they browse. This facility, that we term {\textquoteright}dynamic annotation{\textquoteright}, affords a means of editing Web page content {\textquoteright}on-the-fly{\textquoteright} between the source Web server and the requesting client. Thereby, we have a generic way of modifying the content displayed to local users by addition, removal or reorganising any information sourced from the World-Wide Web, whether this derives from local or remote pages. For some time, we have been exploring the scope for this device and we believe that it affords many potential worthwhile applications. Here, we describe two varieties of use. The first variety focuses on support for individual users in two contexts (second-language support and second language learning). The second variety of use focuses on support for groups of users. These differing applications have a common goal which is content enrichment of the materials placed before the user. Dynamic annotation provides a potent and flexible means to this end.}, keywords = {Content based retrieval, Content enrichment, Dynamic annotation, Information analysis, Knowledge based systems, Learning systems, Servers, Web browsers, World Wide Web}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-8444234304\&partnerID=40\&md5=1ba0d141296de4e5b8bbd76ba0d1d79a}, author = {G.R.S. Weir and Giorgos Lepouras and Costas Vassilakis}, editor = {I. Seruca and J. Filipe and S. Hammoudi and J. Cordeiro} } @conference {571, title = {Distributed Resource Sharing using Self-Organized Peer-to-Peer Networks and Languages from Information Retrieval}, booktitle = {Proceedings of the International Workshop on Self-* Properties in Complex Information Systems (Self-*)}, year = {2004}, month = {May}, address = {Bertinoro, Italy}, author = {Christos Tryfonopoulos and Manolis Koubarakis} } @conference {568, title = {Implementing Publish/Subscribe Systems with Languages from Information Retrieval on Top of Structured Overlay Networks}, booktitle = {Proceedings of the International Workshop on Peer-to-Peer and IR (P2P\&IR @ SIGIR)}, year = {2004}, month = {July}, address = {Sheffield, UK}, author = {Christos Tryfonopoulos and Manolis Koubarakis} } @article {DBLP:journals/eg/VassilakisLRG04, title = {Integrating e-government public transactional services into public authority workflows}, journal = {Electronic Government}, volume = {1}, number = {1}, year = {2004}, pages = {49-60}, abstract = {Documents submitted by citizens through electronic services deployed in the context of e-Government must usually undergo processing by some organisational information system, in order to complete the citizens? requests and for the reply to be returned to the citizen. The integration, however, of the e-service delivery platform and the organisational information system is often hindered for a number of reasons, including security considerations, platform diversity or idiosyncrasies of legacy information systems. In this paper we present a generic method for providing seamless communication between the two platforms, enabling the full integration of documents submitted through electronic services into the organisational workflow, leveraging thus the quality of services offered to the citizens and facilitating e-service development and operation.}, doi = {10.1504/EG.2004.004136}, author = {Costas Vassilakis and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @conference {DBLP:conf/ssdbm/TerrovitisVSBCM04, title = {Modeling and Language Support for the Management of Pattern-Bases}, booktitle = {Proceedings of the 16th International Conference on Scientific and Statistical Database Management (SSDBM 2004), 21-23 June 2004, Santorini Island, Greece}, year = {2004}, pages = {265{\textendash}274}, doi = {10.1109/SSDBM.2004.54}, url = {http://doi.ieeecomputersociety.org/10.1109/SSDBM.2004.54}, author = {Manolis Terrovitis and Panos Vassiliadis and Spiros Skiadopoulos and Elisa Bertino and Barbara Catania and Anna Maddalena} } @conference {576, title = {P2P-DIET: An Extensible P2P Service that Unifies Ad-hoc and Continuous Querying in Super-Peer Networks}, booktitle = {Proceedings of the ACM SIGMOD Conference}, year = {2004}, month = {June}, address = {Paris, France}, author = {Stratos Idreos and Manolis Koubarakis and Christos Tryfonopoulos} } @conference {551, title = {P2P-DIET: One-Time and Continuous Queries in Super-Peer Networks}, booktitle = {Proceedings of the 9th International Conference on Extending Database Technology (EDBT)}, year = {2004}, month = {March}, address = {Heraklion, Greece}, author = {Stratos Idreos and Manolis Koubarakis and Christos Tryfonopoulos} } @proceedings {DBLP:conf/ssdbm/2004, title = {Proceedings of the 16th International Conference on Scientific and Statistical Database Management (SSDBM 2004), 21-23 June 2004, Santorini Island, Greece}, year = {2004}, publisher = {IEEE Computer Society}, isbn = {0-7695-2146-0}, url = {http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=9176} } @conference {585, title = {Publish/Subscribe Systems with Distributed Hash Tables and Languages from Information Retrieval}, booktitle = {Proceedings of the 6th Workshop on Distributed Data and Structures (WDAS)}, year = {2004}, month = {July}, address = {Lausanne, Switzerland}, author = {Christos Tryfonopoulos and Manolis Koubarakis} } @conference {567, title = {Query Processing in Super-Peer Networks with Languages Based on Information Retrieval: the P2P-DIET Approach}, booktitle = {Proceedings of the International Workshop on Peer-to-peer Computing and Databases (P2P\&DB @ EDBT)}, year = {2004}, month = {March}, address = {Herakion, Greece}, author = {Stratos Idreos and Christos Tryfonopoulos and Manolis Koubarakis and Yannis Drougas} } @article {1009361, title = {Real exhibitions in a virtual museum}, journal = {Virtual Reality}, volume = {7}, number = {2}, year = {2004}, pages = {120{\textendash}128}, publisher = {Springer-Verlag}, address = {London, UK}, abstract = {When creating a virtual environment open to the public a number of challenges have to be addressed. The equipment has to be chosen carefully in order to be be able to withstand hard every-day usage, the application has not only to be robust and easy to use, but has also to be appealing to the user, etc. The current paper presents findings gathered from the creation of a multi-thematic virtual museum environment to be offered to visitors of real world museums. A number of design and implementation aspects are described along with an experiment designed to evaluate alternative approaches for implementing the navigation in a virtual museum environment. The paper is concluded with insights gained from the development of the Virtual Museum and portrays future research plans.}, issn = {1359-4338}, doi = {10.1007/s10055-004-0121-5}, url = {https://link.springer.com/article/10.1007/s10055-004-0121-5}, author = {Giorgos Lepouras and Akrivi Katifori and Costas Vassilakis and D. Charitos} } @conference {Lep2004d, title = {Reusability in Electronic Services Development}, booktitle = {Proceedings of the CSITeA 04 conference}, year = {2004}, month = {12}, abstract = {Electronic government employs electronic services to facilitate interaction with citizens and enterprises and deliver a rich and high quality spectrum of services. Development of electronic services can be greatly assisted, both in terms of development cost and roll-out time, by exploiting the reusability inherent in them. Reusability may be promoted by identifying reusable objects in the context of electronic service development, building and populating a repository with such components and providing the means for developers to locate, extract and adapt them to suit the task at hand. In this paper we analyse electronic services to recognise reusable components and present means and techniques that empower electronic service developers to build electronic services through reusable components.}, author = {Costas Vassilakis and Giorgos Lepouras} } @conference {Lepouras_tailorabilityin, title = {Tailorability in the context of E-government Information Systems: An approach}, booktitle = {Proceedings of the IRMA 2004 conference}, year = {2004}, month = {5}, abstract = {The ever changing environment information systems model, and in particular e-government ones, intensifies the need for systems that are able to easily, efficiently and transparently adapt to changing environments. Accommodating unanticipated changes implies that systems must be able to adapt to changes occurring in and evolve in step with their changing environment. Adaptation is concerned with monitoring, analysing and understanding the patterns of the user{\textquoteright}s interaction with the system. Similarly, an information system is said to be evolutionary if it can be purposefully used in a dynamic environment. E-government information systems, in virtue of their nature and function, are driven by the need to adapt and evolve. This suggests that the design and implementation of such systems must provide the necessary infrastructure for evolution and adaptability. In other words, e-government information systems must abide to the Tailorable Information Systems paradigm. In this work we present a case study for the development of a Tailorable e-government information system.}, author = {Giorgos Lepouras and Anya Sotiropoulou and Dimitrios Theotokis and Costas Vassilakis} } @article {Lepouras200596, title = {Virtual museums for all: Employing game technology for edutainment}, journal = {Virtual Reality}, volume = {8}, number = {2}, year = {2004}, note = {cited By (since 1996) 10}, month = {jun}, pages = {96{\textendash}106}, publisher = {Springer Nature}, abstract = {Museums have started to realise the potential of new technologies for the development of edutainment content and services for their visitors. Virtual reality technologies promise to offer a vivid, enjoyable experience to the museums guests, but the cost in time, effort and resources can prove to be overwhelming. In this paper, we propose the use of 3D game technologies for the purpose of developing affordable, easy to use and pleasing virtual environments. To this end, we present a case study based on an already developed version of a virtual museum and a newly implemented version that uses game technologies. The informal assessment indicates that game technologies can offer a prominent and viable solution to the need for affordable desktop virtual reality systems. Β{\textcopyright} Springer-Verlag London Limited 2004.}, doi = {10.1007/s10055-004-0141-1}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-22144472250\&partnerID=40\&md5=c0200e7737345b0757026dbcb3040cf9}, author = {Giorgos Lepouras and Costas Vassilakis} } @article {Maroulis2004267, title = {A web browser for ISDN card phones}, journal = {Journal of Internet Technology}, volume = {5}, number = {3}, year = {2004}, note = {cited By (since 1996) 1}, pages = {267-277}, abstract = {In order to cover the ever-increasing need for more direct and easy access to information, new information access means need to be devised or existing ones need to be further exploited. In this paper, we present a mini Web Browser for ISDN card phones, which enables this widespread device to be used for accessing information in the World Wide Web. The implemented web browser supports HTML and WML pages, while special care was taken to tackle the limitations imposed by the ISDN card phone{\textquoteright}s hardware, such as small screen, limited keyboard, scarce processing and memory resources. One of the techniques employed to increase the capabilities of the ISDN card phone browser was the introduction of a proxy server, which transforms demanding media types to formats that can be handled by the ISDN card phone hardware.}, keywords = {Bandwidth, Costs, Embedded systems, HTML, Information analysis, Integrated multiprotocol, ISDN card phone, Laptop computers, Mobile phones, Personal computers, Personal digital assistants, Proxy servers, Voice/data communication systems, Web browsers}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-4344632311\&partnerID=40\&md5=9242e761d5eedb61880ca004cdaa873d}, author = {Maroulis, D. and Aronis, S. and Nassiapoulou, V. and Grammenos, N. and Costas Vassilakis} } @conference {DBLP:conf/dolap/ManiatisVSV03, title = {Advanced visualization for OLAP}, booktitle = {DOLAP 2003, ACM Sixth International Workshop on Data Warehousing and OLAP, New Orleans, Louisiana, USA, November 7, 2003, Proceedings}, year = {2003}, pages = {9{\textendash}16}, doi = {10.1145/956060.956063}, url = {https://doi.org/10.1145/956060.956063}, author = {Andreas S. Maniatis and Panos Vassiliadis and Spiros Skiadopoulos and Yannis Vassiliou} } @conference {DBLP:conf/dawak/ManiatisVSV03, title = {CPM: A Cube Presentation Model for OLAP}, booktitle = {Data Warehousing and Knowledge Discovery, 5th International Conference, DaWaK 2003, Prague, Czech Republic, September 3-5,2003, Proceedings}, year = {2003}, pages = {4{\textendash}13}, doi = {10.1007/978-3-540-45228-7_2}, url = {https://doi.org/10.1007/978-3-540-45228-7_2}, author = {Andreas S. Maniatis and Panos Vassiliadis and Spiros Skiadopoulos and Yannis Vassiliou} } @proceedings {DBLP:conf/dawak/2003, title = {Data Warehousing and Knowledge Discovery, 5th International Conference, DaWaK 2003, Prague, Czech Republic, September 3-5,2003, Proceedings}, volume = {2737}, year = {2003}, publisher = {Springer}, isbn = {3-540-40807-X}, doi = {10.1007/b11825}, url = {https://doi.org/10.1007/b11825}, editor = {Yahiko Kambayashi and Mukesh K. Mohania and Wolfram W{\"o}{\ss}} } @proceedings {DBLP:conf/dolap/2003, title = {DOLAP 2003, ACM Sixth International Workshop on Data Warehousing and OLAP, New Orleans, Louisiana, USA, November 7, 2003, Proceedings}, year = {2003}, publisher = {ACM}, editor = {Stefano Rizzi and Il-Yeol Song} } @conference {gorilas2003, title = {E-forms services for the Public Sector: Shifting Development Effort from Programmers to Domain Experts}, booktitle = {Proceedings of e-Challenges 2003}, year = {2003}, month = {10}, abstract = {E-forms have a central role in a significant number of e-government services. This paper presents a knowledge-based technical platform aiming to assist public sector employees to generate online transaction services by simplifying their development, maintenance and integration with installed IT systems. At the heart of this platform lies the knowledge and transaction services repository. This repository consists of a number of XML document types that incorporate all necessary details for creating and managing online transaction services. The main underlying idea is to provide a platform with intuitive interfaces that can be used directly by domain experts thus minimising the need for personnel with IT skills. This platform is currently under development within the IST SmartGov project.}, author = {Stelios Gorilas and Costas Vassilakis and Tomas Pariente Lobo and E. Tambouris} } @conference {lep03a, title = {Facilitating VR Museums Web Presence}, booktitle = {Proceedings of HCI 2003}, year = {2003}, month = {6}, pages = {1143{\textendash}1147}, abstract = {The paper presents an environment that enables museum curators to catalogue and publish on the web exhibits in multiple languages and media including 3D, video, images. The system is extendable to accommodate new media types, languages, exhibits, information categories, etc. Visitors have the potential to formulate dynamic personalised exhibit collections using search mechanisms provided by the system.}, author = {Giorgos Lepouras and Akrivi Katifori and Costas Vassilakis and Anna Charissi} } @article {Vassilakis2003315, title = {A framework for managing the lifecycle of transactional e-government services}, journal = {Telematics and Informatics}, volume = {20}, number = {4}, year = {2003}, note = {cited By (since 1996) 13}, pages = {315-329}, abstract = {Filling and submission of electronic forms is a key issue for e-government, since most electronic services offered in this context include some variant of electronic forms. Insofar, IT experts are placed in the centre of electronic forms services lifecycles, undertaking the analysis, design, implementation and maintenance phases. This practice, however, implies various impediments, such as the need for multitudinous teams with diverse skills. In this paper, we present experiences from developing and maintaining a set of electronic services for the Greek Ministry of Finance, and propose an approach to handling electronic services{\textquoteright} lifecycle that balances responsibilities between domain experts and IT professionals. This approach enables a more holistic management of the electronic service lifecycle, by employing modelling and representation in high levels of abstraction and incorporating tools for automatically generating operative service instances from these high-level descriptions. Β{\textcopyright} 2003 Elsevier Science Ltd. All rights reserved.}, keywords = {Communication, Electronic forms, Information science, Information technology}, doi = {10.1016/S0736-5853(03)00011-X}, url = {https://www.sciencedirect.com/science/article/abs/pii/S073658530300011X}, author = {Costas Vassilakis and Laskaridis, G. and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @conference {DBLP:conf/caise/VassilakisLRG03, title = {Improving e-Form Layout Through Analysis of Form Semantics and Validation Checks}, booktitle = {CAiSE Short Paper Proceedings}, year = {2003}, month = {6}, abstract = {Transaction services offered by public authorities vary from simple forms with few fields to multi-form compound documents with hundreds of input areas. In the latter case, field placement within forms is of particular importance for facilitating the filling and error correction processes. In this paper we present an approach to improving the form layout by exploiting validation checks that are usually associated with electronic forms, as well as semantic information that may be attached to form fields by designers.}, url = {http://ceur-ws.org/Vol-74/files/FORUM_38.pdf}, author = {Costas Vassilakis and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @article {577, title = {Selective Information Dissemination in P2P Networks: Problems and Solutions}, journal = {SIGMOD Record, Special Issue on Peer-to-Peer Data Management}, volume = {32}, year = {2003}, pages = {71-76}, author = {Manolis Koubarakis and Christos Tryfonopoulos and Stratos Idreos and Yannis Drougas}, editor = {Karl Aberer} } @proceedings {DBLP:conf/chorochronos/2003, title = {Spatio-Temporal Databases: The CHOROCHRONOS Approach}, volume = {2520}, year = {2003}, publisher = {Springer}, isbn = {3-540-40552-6}, doi = {10.1007/b83622}, url = {https://doi.org/10.1007/b83622}, editor = {Manolis Koubarakis and Timos K. Sellis and Andrew U. Frank and St{\'e}phane Grumbach and Ralf Hartmut G{\"u}ting and Christian S. Jensen and Nikos A. Lorentzos and Yannis Manolopoulos and Enrico Nardelli and Barbara Pernici and Hans-J{\"o}rg Schek and Michel Scholl and Babis Theodoulidis and Nectaria Tryfona} } @conference {DBLP:conf/chorochronos/GrumbachKRSS03, title = {Spatio-temporal Models and Languages: An Approach Based on Constraints}, booktitle = {Spatio-Temporal Databases: The CHOROCHRONOS Approach}, year = {2003}, pages = {177{\textendash}201}, doi = {10.1007/978-3-540-45081-8_5}, url = {https://doi.org/10.1007/978-3-540-45081-8_5}, author = {St{\'e}phane Grumbach and Manolis Koubarakis and Philippe Rigaux and Michel Scholl and Spiros Skiadopoulos} } @article {Lepouras2003248, title = {A system to support dissemination of knowledge and sharing of experiences in the working environment: Review Code 066}, journal = {International Journal of Continuing Engineering Education and Lifelong Learning}, volume = {13}, number = {3/4}, year = {2003}, pages = {248-257}, publisher = {Inderscience Publishers}, abstract = {In the information era, enterprises strive to be productive and efficient. One feature of this goal is for employers to engage their employees in education programs, to help them to gain new experiences and knowledge and to adapt to an ever-changing working environment. Such programs must be carefully designed in order to achieve satisfactory results. Recently, enterprises, recognising the role that technology can play in the education of their employees, have adopted systems that supplement the traditional educational model with mechanisms that enable the sharing of experiences and knowledge. In this paper we describe an architecture and a system prototype that allows users to search easily for information, interact with colleagues and share experiences, and to compose and disseminate best practices and knowledge. The design of this system is based on insights gained from the operation of the Greek taxation system.}, keywords = {Education computing, Engineering education, Information dissemination, Integrated systems, Knowledge based systems, Systems analysis}, doi = {10.1504/ijceell.2003.003277}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-0041975974\&partnerID=40\&md5=3fdaf5e728f5571c01c70507e0ad7004}, author = {Giorgos Lepouras and Costas Vassilakis and G.R.S. Weir} } @proceedings {DBLP:conf/caise/2002, title = {Advanced Information Systems Engineering, 14th International Conference, CAiSE 2002, Toronto, Canada, May 27-31, 2002, Proceedings}, volume = {2348}, year = {2002}, publisher = {Springer}, isbn = {3-540-43738-X}, doi = {10.1007/3-540-47961-9}, url = {https://doi.org/10.1007/3-540-47961-9}, editor = {Anne Banks Pidduck and John Mylopoulos and Carson C. Woo and M. Tamer {\"O}zsu} } @conference {DBLP:conf/dolap/VassiliadisSS02, title = {Conceptual modeling for ETL processes}, booktitle = {DOLAP 2002, ACM Fifth International Workshop on Data Warehousing and OLAP, November 8, 2002, McLean, VA, USA, Proceedings}, year = {2002}, pages = {14{\textendash}21}, doi = {10.1145/583890.583893}, url = {https://doi.org/10.1145/583890.583893}, author = {Panos Vassiliadis and Alkis Simitsis and Spiros Skiadopoulos} } @conference {DBLP:conf/cp/SkiadopoulosK02, title = {Consistency Checking for Qualitative Spatial Reasoning with Cardinal Directions}, booktitle = {Principles and Practice of Constraint Programming - CP 2002, 8th International Conference, CP 2002, Ithaca, NY, USA, September 9-13, 2002, Proceedings}, year = {2002}, pages = {341{\textendash}355}, doi = {10.1007/3-540-46135-3_23}, url = {https://doi.org/10.1007/3-540-46135-3_23}, author = {Spiros Skiadopoulos and Manolis Koubarakis} } @conference {756327, title = {Controlled Caching of Dynamic WWW Pages}, booktitle = {DEXA {\textquoteright}02: Proceedings of the 13th International Conference on Database and Expert Systems Applications}, year = {2002}, month = {9}, pages = {9{\textendash}18}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Web sites employ dynamically generated pages for content delivery more and more often, in order to increase their flexibility and provide up-to-date information. This practice, however, increases server load dramatically, since each request results to the execution of code, which may involve processing and/or access to information repositories. In this paper we present a scheme for maintaining a server-side cache of dynamically generated pages, allowing for cache consistency maintenance, without placing heavy burdens on application programmers. We also present insights to architecture scalability and some results obtained from conducted experiments.}, isbn = {3-540-44126-3}, doi = {10.1007/3-540-46146-9_2}, url = {http://link.springer.com/chapter/10.1007\%2F3-540-46146-9_2}, author = {Costas Vassilakis and Giorgos Lepouras} } @conference {536, title = {Data Models and Languages for Agent-Based Textual Information Dissemination}, booktitle = {Proceedings of the 6th International Workshop on Cooperative Information Agents (CIA)}, year = {2002}, month = {September}, publisher = {Springer}, organization = {Springer}, address = {Madrid, Spain}, author = {Manolis Koubarakis and Christos Tryfonopoulos and Paraskevi Raftopoulou and Theodoros Koutris} } @proceedings {DBLP:conf/dmdw/2002, title = {Design and Management of Data Warehouses 2002, Proceedings of the 4th Intl. Workshop DMDW{\textquoteright}2002, Toronto, Canada, May 27, 2002}, volume = {58}, year = {2002}, publisher = {CEUR-WS.org}, url = {http://ceur-ws.org/Vol-58}, editor = {Laks V. S. Lakshmanan} } @proceedings {DBLP:conf/dolap/2002, title = {DOLAP 2002, ACM Fifth International Workshop on Data Warehousing and OLAP, November 8, 2002, McLean, VA, USA, Proceedings}, year = {2002}, publisher = {ACM}, isbn = {1-58113-590-4}, editor = {Il-Yeol Song and Dimitri Theodoratos} } @conference {572, title = {Efficient Agent-Based Dissemination of Textual Information}, booktitle = {Proceedings of the 2nd Hellenic Conference on Artificial Intelligence (SETN)}, year = {2002}, month = {April}, address = {Thessaloniki, Greece}, author = {Manolis Koubarakis and Theodoros Koutris and Paraskevi Raftopoulou and Christos Tryfonopoulos} } @conference {546, title = {Information Alert in Distributed Digital Libraries: The Models, Languages, and Architecture of DIAS}, booktitle = {Proceedings of the 6th European Conference on Research and Advanced Technology for Digital Libraries (ECDL)}, year = {2002}, month = {September}, address = {Rome, Italy}, author = {Manolis Koubarakis and Theodoros Koutris and Christos Tryfonopoulos and Paraskevi Raftopoulou} } @conference {DBLP:conf/caise/VassiliadisSS02, title = {On the Logical Modeling of ETL Processes}, booktitle = {Advanced Information Systems Engineering, 14th International Conference, CAiSE 2002, Toronto, Canada, May 27-31, 2002, Proceedings}, year = {2002}, pages = {782{\textendash}786}, doi = {10.1007/3-540-47961-9_67}, url = {https://doi.org/10.1007/3-540-47961-9_67}, author = {Panos Vassiliadis and Alkis Simitsis and Spiros Skiadopoulos} } @conference {DBLP:conf/dmdw/VassiliadisSS02, title = {Modeling ETL activities as graphs}, booktitle = {Design and Management of Data Warehouses 2002, Proceedings of the 4th Intl. Workshop DMDW{\textquoteright}2002, Toronto, Canada, May 27, 2002}, year = {2002}, pages = {52{\textendash}61}, url = {http://ceur-ws.org/Vol-58/simitsis.pdf}, author = {Panos Vassiliadis and Alkis Simitsis and Spiros Skiadopoulos} } @conference {667640, title = {An Object-Oriented Approach for Designing Administrative E-forms and Transactional E-services}, booktitle = {OOIS {\textquoteright}02: Proceedings of the 8th International Conference on Object-Oriented. Information Systems}, year = {2002}, month = {9}, pages = {19{\textendash}30}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Although electronic transaction services are considered to be a necessity for e-government, it has not been possible insofar to unleash their full potential. E-forms are central to the development of e-government, being a basic means for implementing the majority of the public services considered as required for local and central public administration authorities. In this paper, we present an object-oriented model for e-form-based administrative services, which spans the e-service lifecycle, including development, deployment and use by enterprises and citizens, data collection and communication with legacy information systems. The proposed approach encompasses semantic, structural and active aspects of e-forms, providing thus an inclusive framework for modelling electronic services.}, isbn = {3-540-44087-9}, doi = {10.1007/3-540-46102-7_6}, author = {D. Gouscos and S. Rouvas and Costas Vassilakis and P. Georgiadis} } @conference {584, title = {Peer-to-peer Agent Systems for Textual Information Dissemination: Algorithms and Complexity}, booktitle = {Proceedings of the UK Workshop on Multiagent Systems (UKMAS)}, year = {2002}, month = {December}, address = {Liverpool, UK}, author = {Manolis Koubarakis and Christos Tryfonopoulos} } @proceedings {DBLP:conf/cp/2002, title = {Principles and Practice of Constraint Programming - CP 2002, 8th International Conference, CP 2002, Ithaca, NY, USA, September 9-13, 2002, Proceedings}, volume = {2470}, year = {2002}, publisher = {Springer}, isbn = {3-540-44120-4}, doi = {10.1007/3-540-46135-3}, url = {https://doi.org/10.1007/3-540-46135-3}, editor = {Pascal Van Hentenryck} } @conference {649749, title = {Serving Enhanced Hypermedia Information}, booktitle = {Proceedings of the 24th BCS-IRSG European Colloquium on IR Research}, year = {2002}, month = {3}, pages = {86{\textendash}92}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {An apparent limitation of existing Web pages is their inability to accommodate differences in the interests and needs of individual users. The present paper describes an approach that dynamically customises the content of public Web-based information via an interceding {\textquoteright}enhancement server{\textquoteright}. The design and operation of this system is described with examples drawn from two current versions. Indications from early trials support the view that this approach affords considerable scope for accommodating the needs and interests of individual Web users.}, isbn = {3-540-43343-0}, doi = {10.1007/3-540-45886-7_6}, author = {Giorgos Lepouras and Costas Vassilakis and G.R.S. Weir} } @conference {lep2002a1, title = {SMARTGOV: A Governmental Knowledge-based Platform for Public Sector Online Services}, booktitle = {Proceedings KMGov2002}, year = {2002}, month = {5}, pages = {173{\textendash}185}, address = {Copenhagen, Denmark}, abstract = {Public transaction services (such as e-forms), although perceived the future of e-government have not yet realised their full potential. E-forms have a significant role in e-government, as they are the basis for realising most of the twenty public services that all European Union member states have to provide to their citizens and businesses. The aim of this paper is to present a knowledge-based platform to assist public sector employees to generate online transaction services by simplifying their development, maintenance and integration with already installed IT systems.}, author = {E. Tambouris and G. Boukis and Costas Vassilakis and Giorgos Lepouras and S. Rouvas and Canadas, R. and Heredia, S. and Lopez Usero, J. C.} } @conference {Georgiadis_2002, title = {SmartGov: A Knowledge-Based Platform for Transactional Electronic Services}, booktitle = {Lecture Notes in Computer Science}, year = {2002}, month = {9}, pages = {362-369}, publisher = {Springer Berlin Heidelberg}, organization = {Springer Berlin Heidelberg}, abstract = {Public transaction services (such as e-forms) although perceived the future of e-government have not yet realised their full potential. E-forms have a significant role in e-government, as they are the basis for implementing most of the twenty public services that all member states have to provide to their citizens and businesses. The aim of the SmartGov project is to specify, develop, deploy and evaluate a knowledge-based platform to assist public sector employees to generate online transaction services by simplifying their development, maintenance and integration with already installed IT systems. This platform will be evaluated in two European countries (in one Ministry and one Local Authority). This paper outlines key issues in the development of the SmartGov system platform.}, doi = {10.1007/978-3-540-46138-8_59}, url = {https://link.springer.com/chapter/10.1007/978-3-540-46138-8_59}, author = {P. Georgiadis and Giorgos Lepouras and Costas Vassilakis and G. Boukis and E. Tambouris and S. Gorilas and E. Davenport and A. Macintosh and J. Fraser and D. Lochhead} } @conference {650426, title = {Transactional e-Government Services: An Integrated Approach}, booktitle = {EGOV {\textquoteright}02: Proceedings of the First International Conference on Electronic Government}, year = {2002}, month = {9}, pages = {276{\textendash}279}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Although form-based transactional services are fundamental to electronic government activities, their widespread does neither meet the citizen{\textquoteright}s expectations, nor the potential offered by state-of-the-art technologies. Besides any bureaucratic impediments, the primary reason for this is that traditional software engineering approaches cannot satisfactorily handle all the aspects of electronic services lifecycle. In this paper we present experiences from developing and maintaining a set of electronic services for the Greek Ministry of Finance, and propose a new approach for handling electronic service projects. The proposed approach has been successfully employed for developing extensions to the existing services, as well as some new ones.}, isbn = {3-540-44121-2}, doi = {10.1007/978-3-540-46138-8_44}, url = {http://link.springer.com/chapter/10.1007\%2F978-3-540-46138-8_44}, author = {Costas Vassilakis and Laskaridis, G. and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @proceedings {DBLP:conf/ssd/2001, title = {Advances in Spatial and Temporal Databases, 7th International Symposium, SSTD 2001, Redondo Beach, CA, USA, July 12-15, 2001, Proceedings}, volume = {2121}, year = {2001}, publisher = {Springer}, isbn = {3-540-42301-X}, doi = {10.1007/3-540-47724-1}, url = {https://doi.org/10.1007/3-540-47724-1}, editor = {Christian S. Jensen and Markus Schneider and Bernhard Seeger and Vassilis J. Tsotras} } @conference {599, title = {Agents in Decentralised Information Ecosystems: The DIET Approach}, booktitle = {Symposium on Information Agents for E-Commerce, AISB Convention}, year = {2001}, month = {March}, address = {University of York, United Kingdom}, abstract = {The complexity of the current global information infrastructure requires novel means of understanding and exploiting the dynamics of information. One means may be through the concept of an information ecosystem. An information ecosystem is analogous to a natural ecosystem in which there are flows of materials and energy analogous to information flow between many interacting individuals. This paper describes a multi-agent platform, DIET (Decentralised Information Ecosystem Technologies) that can be used to implement open, robust, adaptive and scalable ecosystem-inspired systems. We describe the design principles of the DIET software architecture, and present a simple example application based upon it. We go on to consider how the DIET system can be used to develop information brokering agents, and how these can contribute to the implementation of economic interactions between agents, as well as identifying some open questions relating to research in these areas. In this way we show the capacity of the DIET system to support applications using information agents.}, author = {P. Marrow and Manolis Koubarakis and R.H. van Lengen and F. Valverde-Albacete and E. Bonsma and J. Cid-Suerio and A.R. Figueiras-Vidal and A. Gallardo-Antolin and C. Hoile and T. Koutris and H. Molina-Bulla and A. Navia-Vazquez and Paraskevi Raftopoulou and N. Skarmeas and Christos Tryfonopoulos and F. Wang and C. Xiruhaki} } @conference {aisb01-MKL+, title = {Agents in Decentralised Information Ecosystems: The DIET Approach}, booktitle = {Proccedings of the Symposium on Information Agents for E-Commerce, AISB Convention}, year = {2001}, month = {March}, pages = {109{\textendash}117}, address = {York, UK}, author = {P. Marrow and Manolis Koubarakis and R.H. van Lengen and F. Valverde-Albacete and E. Bonsma and J. Cid-Suerio and A.R. Figueiras-Vidal and A. Gallardo-Antolin and C. Hoile and T. Koutris and H. Molina-Bulla and A. Navia-Vazquez and Paraskevi Raftopoulou and N. Skarmeas and Christos Tryfonopoulos and F. Wang and C. Xiruhaki} } @article {DBLP:journals/is/VassiliadisVSKS01, title = {ARKTOS: towards the modeling, design, control and execution of ETL processes}, journal = {Inf. Syst.}, volume = {26}, number = {8}, year = {2001}, pages = {537{\textendash}561}, doi = {10.1016/S0306-4379(01)00039-4}, url = {https://doi.org/10.1016/S0306-4379(01)00039-4}, author = {Panos Vassiliadis and Zografoula Vagena and Spiros Skiadopoulos and Nikos Karayannidis and Timos K. Sellis} } @conference {Lep01a, title = {Building a VR - Museum in a Museum}, booktitle = {Proceedings of the Third International Virtual Reality Conference, VRIC2001}, year = {2001}, month = {5}, abstract = {Past years have seen the exploitation of multimedia techniques and lately the introduction of virtual reality methods to create new forms of presentation for museums{\textquoteright} exhibitions. Virtual Reality can offer a number of advantages to museums, offering a way to overcome some common problems like the lack of space or the need of visitors to interact with the exhibits. A broad categorisation of virtual museums reveals that they vary from fully immersive cave systems to simple multimedia presentations. In our approach to develop a virtual reality museum we have designed a virtual environment (VE) where guests can visit a total of ten different museums. The processes of digitisation, architectural design and exhibit presentation are outlined and points of particular importance are explained. Exhibits from the real world museums have been digitised and integrated in the VE. The system has been implemented in two versions: one fully immersive and one with a stereo display.}, author = {Giorgos Lepouras and D. Charitos and Costas Vassilakis and Charissi, A. and Halatsi, L.} } @conference {DBLP:conf/ssd/SkiadopoulosK01, title = {Composing Cardinal Direction Relations}, booktitle = {Advances in Spatial and Temporal Databases, 7th International Symposium, SSTD 2001, Redondo Beach, CA, USA, July 12-15, 2001, Proceedings}, year = {2001}, pages = {299{\textendash}320}, doi = {10.1007/3-540-47724-1_16}, url = {https://doi.org/10.1007/3-540-47724-1_16}, author = {Spiros Skiadopoulos and Manolis Koubarakis} } @conference {Charitos2001284, title = {Designing a virtual museum within a museum}, booktitle = {Proceedings VAST 2001 Virtual Reality, Archeology, and Cultural Heritage}, year = {2001}, note = {cited By (since 1996) 0}, month = {11}, pages = {284}, abstract = {The designing of a virtual museum within a museum was discussed. In regard with it, the Virtual Museum project sponsored by the Greek General Secretariat of Research and Technology was presented. The project{\textquoteright}s main objective was to create a virtual environment (VE) for enhancing the experience of visiting a museum by affording view and manipulation of certain exhibits.}, keywords = {Information retrieval systems, Internet, Museums, Technical presentations, Three dimensional computer graphics, Virtual museum, Virtual reality}, doi = {10.1145/584993.585043}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-0141426770\&partnerID=40\&md5=50066081a4e5d55bfc3c823813535add}, author = {D. Charitos and Giorgos Lepouras and Costas Vassilakis and Akrivi Katifori and Charissi, A. and Halatsi, L.}, editor = {S. N. Spencer} } @conference {Lask2001a, title = {e-Citizens and e-Consumers: Is There a Difference?}, booktitle = {Proceedings of the PCHCI 2001 Workshop: "Transforming Web Surfers to E-Shoppers"}, year = {2001}, month = {12}, pages = {47-50}, abstract = {Both the business sector and the government are nowadays embracing Internet technologies in order to provide high quality on-line services to their "target groups". In both cases, service providers are trying to transform web surfers, casually visiting their web sites to seek information, to users of their electronic services, i.e. e-consumers and. e-citizens. In this paper, we address the similarities and the differences between the business and the government, when they act as service providers, with respect to the factors for successful service and the issues that must be addressed.}, author = {Laskaridis, G. and Costas Vassilakis and Giorgos Lepouras and S. Rouvas} } @proceedings {DBLP:conf/caise/2000, title = {Advanced Information Systems Engineering, 12th International Conference CAiSE 2000, Stockholm, Sweden, June 5-9, 2000, Proceedings}, volume = {1789}, year = {2000}, publisher = {Springer}, isbn = {3-540-67630-9}, doi = {10.1007/3-540-45140-4}, url = {https://doi.org/10.1007/3-540-45140-4}, editor = {Benkt Wangler and Lars Bergman} } @conference {Dimitrios00anapproach, title = {An Approach to Designing and Implementing Virtual Museums}, booktitle = {Proceedings of the seventh UK VR-SIG Conference}, year = {2000}, month = {9}, abstract = {The current paper describes an approach to designing and implementing a virtual environment comprising ten different museums. The number of museums as well as the variety of their exhibits lead to the adoption of a generalised strategy that catered for all museum presentation needs and allowed for future expansion. Furthermore, the system architecture supports the delivery of multimedia content either over the Internet or via a local immersive virtual reality installation.}, author = {D. Charitos and Giorgos Lepouras and Costas Vassilakis and Akrivi Katifori and C. Halatsis} } @article {DBLP:journals/debu/VassiliadisVSK00, title = {ARKTOS: A Tool For Data Cleaning and Transformation in Data Warehouse Environments}, journal = {IEEE Data Eng. Bull.}, volume = {23}, number = {4}, year = {2000}, pages = {42{\textendash}47}, url = {http://sites.computer.org/debull/A00DEC-CD.pdf}, author = {Panos Vassiliadis and Zografoula Vagena and Spiros Skiadopoulos and Nikos Karayannidis} } @article {Kovacs2000417, title = {Function oriented history representation in databases}, journal = {Computers and Artificial Intelligence}, volume = {19}, number = {5}, year = {2000}, note = {cited By (since 1996) 0}, pages = {417-444}, abstract = {In the past years the management of temporal data has attracted numerous researchers resulting to a large number of temporal data extensions to the relational and object oriented data models. In this paper, the proposed temporal data model focuses on the functional characteristics of the histories. The paper introduces a set oriented description of the calendars together with a function oriented history concept with a history-algebra. The completeness of the proposed model with respect to the reduced temporal algebra TA is also proven. The expressive power of the proposed model is demonstrated in the end of the paper by a hospital example.}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-33751245138\&partnerID=40\&md5=575f314a008c5f0b9ae258689c3de7be}, author = {Kovacs, L. and Costas Vassilakis} } @conference {DBLP:conf/caise/VassiliadisS00, title = {Modelling and Optimisation Issues for Multidimensional Databases}, booktitle = {Advanced Information Systems Engineering, 12th International Conference CAiSE 2000, Stockholm, Sweden, June 5-9, 2000, Proceedings}, year = {2000}, pages = {482{\textendash}497}, doi = {10.1007/3-540-45140-4_32}, url = {https://doi.org/10.1007/3-540-45140-4_32}, author = {Panos Vassiliadis and Spiros Skiadopoulos} } @conference {Lep2000a, title = {Multilingual Web Site Construction and Maintenance}, booktitle = {Proceedings of the SCI 2000 conference}, year = {2000}, month = {7}, pages = {56-61}, abstract = {The construction of multilingual web sites is probably the best answer to addressing the problem of the diverse cultural background of the Internet community. However, developing multiple instances of the same site in different languages induces increased overhead for both the implementation and the maintenance phase. The paper reviews current techniques and describes an alternative to constructing multilingual web sites, which eases the development and maintenance phases, without possessing any of the drawbacks of existing tools. The paper concludes proposing possible future enhancements.}, author = {Giorgos Lepouras and Costas Vassilakis} } @article {Vassilakis200038, title = {An optimisation scheme for coalesce/valid time selection operator sequences}, journal = {SIGMOD Record (ACM Special Interest Group on Management of Data)}, volume = {29}, number = {1}, year = {2000}, note = {cited By (since 1996) 4}, pages = {38-43}, abstract = {Queries in temporal databases often employ the coalesce operator, either to coalesce results of projections, or data which are not coalesced upon storage. Therefore, the performance and the optimisation schemes utilised for this operator is of major importance for the performance of temporal DBMSs. Insofar, performance studies for various algorithms that implement this operator have been conducted, however, the joint optimisation of the coalesce operator with other algebraic operators that appear in the query execution plan has only received minimal attention. In this paper, we propose a scheme for combining the coalesce operator with selection operators which are applied to the valid time of the tuples produced from a coalescing operation. The proposed scheme aims at reducing the number of tuples that a coalescing operator must process, while at the same time allows the optimiser to exploit temporal indices on the valid time of the data.}, doi = {10.1145/344788.344803}, url = {https://dl.acm.org/citation.cfm?id=344803}, author = {Costas Vassilakis} } @article {DBLP:journals/ai/KoubarakisS00, title = {Querying temporal and spatial constraint networks in PTIME}, journal = {Artif. Intell.}, volume = {123}, number = {1-2}, year = {2000}, pages = {223{\textendash}263}, doi = {10.1016/S0004-3702(00)00055-2}, url = {https://doi.org/10.1016/S0004-3702(00)00055-2}, author = {Manolis Koubarakis and Spiros Skiadopoulos} } @conference {797082, title = {Distributed Information Systems Tailorability: A Component Approach}, booktitle = {FTDCS {\textquoteright}99: Proceedings of the 7th IEEE Workshop on Future Trends of Distributed Computing Systems}, year = {1999}, month = {12}, pages = {95}, publisher = {IEEE Computer Society}, organization = {IEEE Computer Society}, address = {Washington, DC, USA}, abstract = {Distributed software systems need to evolve according to the ever-changing requirements on which they were built. Software systems{\textquoteright} tailorability can be achieved in terms of component software. Atoms and molecules the basic constructs of the ATOMA framework are the building blocks for distributed tailorable component-based software systems. These constructs can be considered as independent agents, that communicate in terms of unanticipated, connections that are established at runtime, thus forming agent communities. System tailorability can take place at two levels. In high level tailorability whole parts of the functionality of a system, represented as agents, can be altered in order to provide new functionality. At a lower level, the tailorability of an agent itself that is the tailorability of its functionality, is achieved through a flexible service mapping implementation for rule-based method invocation.}, isbn = {0-7695-0468-X}, doi = {10.1109/FTDCS.1999.818790}, author = {Dimitrios Theotokis and Kapos, G. D. and Costas Vassilakis and Anya Sotiropoulou and Gyftodimos, G.} } @proceedings {DBLP:conf/aaai/1999, title = {Proceedings of the Sixteenth National Conference on Artificial Intelligence and Eleventh Conference on Innovative Applications of Artificial Intelligence, July 18-22, 1999, Orlando, Florida, USA}, year = {1999}, publisher = {AAAI Press / The MIT Press}, isbn = {0-262-51106-1}, url = {http://www.aaai.org/Conferences/AAAI/aaai99.php}, editor = {Jim Hendler and Devika Subramanian} } @conference {DBLP:conf/aaai/KoubarakisS99, title = {Querying Temporal Constraint Networks in PTIME}, booktitle = {Proceedings of the Sixteenth National Conference on Artificial Intelligence and Eleventh Conference on Innovative Applications of Artificial Intelligence, July 18-22, 1999, Orlando, Florida, USA.}, year = {1999}, pages = {745{\textendash}750}, url = {http://www.aaai.org/Library/AAAI/1999/aaai99-106.php}, author = {Manolis Koubarakis and Spiros Skiadopoulos} } @conference {vassil99a, title = {Is Server-Side Programming Killing Your Web Server?}, booktitle = {Proceedings of the ActiveWeb 99 Conference}, year = {1999}, month = {10}, address = {Staffordshire University}, abstract = {The paper addresses issues related to client/server technologies and specifically the effectiveness of server-side programming techniques. The motive for this study was the need to create a lightweight and dynamic navigational aid for use in a web site. Towards this goal a number of possible solutions were considered and for two of them an experiment was run to determine the best suited for our case. The rest of the paper outlines our findings.}, url = {http://www.visualize-uk.com/conf/activeweb/proceed/pap7/}, author = {Costas Vassilakis and Giorgos Lepouras} } @proceedings {DBLP:conf/stdbm/1999, title = {Spatio-Temporal Database Management, International Workshop STDBM{\textquoteright}99, Edinburgh, Scotland, September 10-11, 1999, Proceedings}, volume = {1678}, year = {1999}, publisher = {Springer}, isbn = {3-540-66401-7}, doi = {10.1007/3-540-48344-6}, url = {https://doi.org/10.1007/3-540-48344-6}, editor = {Michael H. B{\"o}hlen and Christian S. Jensen and Michel Scholl} } @conference {DBLP:conf/stdbm/KoubarakisS99, title = {Tractable Query Answering in Indefinite Constraint Databases: Basic Results and Applications to Querying Spatiotemporal Information}, booktitle = {Spatio-Temporal Database Management, International Workshop STDBM{\textquoteright}99, Edinburgh, Scotland, September 10-11, 1999, Proceedings}, year = {1999}, pages = {204{\textendash}223}, doi = {10.1007/3-540-48344-6_12}, url = {https://doi.org/10.1007/3-540-48344-6_12}, author = {Manolis Koubarakis and Spiros Skiadopoulos} } @article {Vassilakis1998335, title = {Implementation of transaction and concurrency control support in a temporal DBMS}, journal = {Information Systems}, volume = {23}, number = {5}, year = {1998}, note = {cited By (since 1996) 2}, pages = {335{\textendash}350}, abstract = {Transactions and concurrency control are significant features in database systems, facilitating functions both at user and system level. However, the support of these features in a temporal DBMS has not yet received adequate research attention. In this paper, we describe the techniques developed in order to support transaction and concurrency control in a temporal DBMS that was implemented as an additional layer to a commercial DBMS. The proposed techniques make direct use of the transaction mechanisms of the DBMS. In addition, they overcome a number of limitations such as automatic commit points, lock release and log size increment, which are imposed by the underlying DBMS. Our measurements have shown that the overhead introduced by these techniques is negligible, less than 1\% in all cases. The approach undertaken is of general interest, it can also be applied to non-temporal DBMS extensions. Copyright Β{\textcopyright} 1998 Elsevier Science Ltd. All rights reserved.}, keywords = {Concurrency control, Data structures, Database systems, Temporal databases}, doi = {10.1016/S0306-4379(98)00015-5}, url = {https://doi.org/10.1016/S0306-4379(98)00015-5}, author = {Costas Vassilakis and N. Lorentzos and P. Georgiadis} } @conference {754888, title = {Implementing Embedded Valid Time Query Languages}, booktitle = {DEXA {\textquoteright}98: Proceedings of the 9th International Conference on Database and Expert Systems Applications}, year = {1998}, month = {8}, pages = {561{\textendash}572}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Application development on top of database systems is heavily based on the existence of embedded and 4GL languages. However, the issue of designing and implementing embedded or 4GL temporal languages has not been addressed insofar. In this paper, we present a design approach for implementing an embedded temporal language that supports valid time. Furthermore, we introduce implementation techniques that can be used for implementing any embedded temporal language that supports valid time on top of a DBMS.}, isbn = {3-540-64950-6}, doi = {10.1007/BFb0054514}, author = {Costas Vassilakis and P. Georgiadis and Sellis, Timos K.} } @conference {DBLP:conf/iadt/SotiropoulouSV98, title = {Temporal Extension to ODMG}, booktitle = {IADT}, year = {1998}, month = {7}, pages = {304-311}, abstract = {In the past years a number of temporal extensions to the different database models have been proposed. Extensions to the relational model have been following the different SQL standards, while no attempts have been made to extend the OO-databases{\textquoteright} standard, defined by ODMG. In this paper we present a temporal extension to the ODMG standard, as this has been specified in the TOOBIS project. A Temporal Object Data Model, a Temporal Object Definition Language and a Temporal Object Query Language have been specified and have been proposed as extensions to the ODM, ODL and OQL of ODMG. This extension has been implemented over a commercial OODBMS, reinforcing and validating the effort of standardisation and portability of this extension.}, author = {Anya Sotiropoulou and Michael Souillard and Costas Vassilakis} } @conference {DBLP:conf/inforsid/SouillardVS98, title = {TOOBIS: Application de la gestion de donn{\'e}es temporelles dans le domaine de la recherche clinique}, booktitle = {INFORSID}, year = {1998}, month = {5}, pages = {147-165}, abstract = {Les donn?es temporelles, c{\textquoteright}est-?-dire des donn?es ?voluant dans le temps et pour lesquelles il est int?ressant de maintenir un historique des valeurs, ne sont pas utilis?es dans l{\textquoteright}industrie. Mais cela ne veut pas dire pour autant que les diverses applications existantes ne g?rent que des donn?es non temporelles. En fait, des donn?es temporelles doivent ?tre g?r?es par un grand nombre d{\textquoteright}applications et de secteurs industriels tels que la finance, l{\textquoteright}assurance, le suivi m?dical, les services de r?servation, etc. Ces applications utilisent le plus souvent le r?sultat de d?veloppements internes simulant des donn?es temporelles, qui peuvent ?tre co?teux. Le march? des solutions pour manipuler des donn?es temporelles est encore limit?, et ne r?pond pas ? tous les besoins. Cet article pr?sente les r?sultats du projet europ?en TOOBIS - Temporal Object Oriented dataBase within Information System - en mettant l{\textquoteright}accent sur une application g?rant des donn?es temporelles, d?velopp?e dans le domaine de la Recherche Clinique. TOOBIS propose une extension du standard des bases de donn?es orient?es objet afin de fournir un syst?me de gestion des bases de donn?es temporelles complet, ainsi qu{\textquoteright}une m?thodologie de conception temporelle.}, author = {Michael Souillard and Costas Vassilakis and Anya Sotiropoulou} } @conference {790099, title = {A comparative study of temporal DBMS architectures}, booktitle = {DEXA {\textquoteright}96: Proceedings of the 7th International Workshop on Database and Expert Systems Applications}, year = {1996}, month = {9}, pages = {153}, publisher = {IEEE Computer Society}, organization = {IEEE Computer Society}, address = {Washington, DC, USA}, abstract = {In the past years, a number of implementations of temporal DBMSs has been reported. Most of these implementations share a common feature, which is that they have been built as an extension to a snapshot DBMS. In this paper, we present three alternative design approaches that can be used for extending a snapshot DBMS to support temporal data,and evaluate the suitability of each approach, with respect to a number of design objectives.}, isbn = {0-8186-7662-0}, doi = {10.1109/DEXA.1996.558289}, author = {Costas Vassilakis and P. Georgiadis and Anya Sotiropoulou} } @article {Spiliopoulou1996341, title = {A cost model for the estimation of query execution time in a parallel environment supporting pipeline}, journal = {Computers and Artificial Intelligence}, volume = {15}, number = {4}, year = {1996}, note = {cited By (since 1996) 3}, pages = {341-368}, abstract = {We propose a model for the estimation of query execution time in an environment supporting bushy and pipelined parallelism. We consider a parallel architecture of processors having private main memories, accessing a shared secondary storage and communicating to each other via a network. For this environment, we compute the cost of query operators when processed in isolation and when in pipeline mode. We use those formulae to incrementally compute the cost of a query execution plan from its components. Our cost model can be incorporated to any optimizer for parallel query processing that considers parallel and pipelined execution of the query operators.}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-33747804589\&partnerID=40\&md5=e04ec1604249525ebaf3dfb111a34f12}, author = {M. Spiliopoulou and M. Hatzopoulos and Costas Vassilakis} } @conference {719700, title = {Transaction Support in a Temporal DBMS}, booktitle = {Proceedings of the International Workshop on Temporal Databases}, year = {1995}, month = {9}, pages = {255{\textendash}271}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Transactions are a significant concept in database systems, facilitating functions both at user and system level. However transaction support in temporal DBMSs has not yet received enough research attention. In this paper, we present techniques for incorporating transaction support in a temporal DBMS, which is implemented as an additional layer to a commercial RDBMS. These techniques overcome certain limitations imposed by the underlying RDBMS, and avoid excessive increment of the log size.}, isbn = {3-540-19945-4}, doi = {10.1007/978-1-4471-3033-8_14}, url = {http://link.springer.com/chapter/10.1007\%2F978-1-4471-3033-8_14}, author = {Costas Vassilakis and N. Lorentzos and P. Georgiadis} } @conference {1993-kassapidis-hci, title = {Comparative Study of Protocols of the Transport Layer for Multimedia Applications}, booktitle = {Proceedings of the 4th Hellenic Conference on Informatics}, year = {1993}, month = {12}, pages = {105-118}, abstract = {The forthcoming use of multimedia applications will require powerful computers and high performance networks. While great progress has been made to the physical layer of networks, the upper software layers of the OSI reference model have not kept up pace with them. This paper presents the demands imposed by multimedia applications on the underlying networks and their mapping to transport layer services, that protocols implementing it must provide. Four well-known transport layer protocols are briefly presented (TCP, TP4, VMTP, HSTP/XTP). The mechanisms employed by each one of those are studied and their suitability for demanding multimedia environments are evaluated. We conclude that much more effort needs to be made on the transport layer protocols so that high performance network architectures will be available to fullfill the diverse requirements of tomorrow{\textquoteright}s multimedia applications.}, url = {http://cst.uop.gr/images/papers/1993-kassapidis-hci.pdf}, author = {Kassapidis, P. and Costas Vassilakis and M. Nikolaidou and P. Georgiadis and Votsis, Gr. and Pronios, N.} } @conference {1993-boukouvalas-hci, title = {An Enhanced System for File Access in a Distributed UNIX Environment}, booktitle = {Proceedings of the 4th Hellenic Conference on Informatics}, year = {1993}, month = {12}, abstract = {In this study we present an Enhanced File System for a Distributed Unix Environment. The Enhanced Unix File System implements a flexible protection mechanism for files and directories. It is based on the concept of Access Control Lists (ACL), which allows different permissions for files and directories to be given to specific users. His work was developed under the SunOS/NFS distributed environment, using Remote Procedure Calls (RPC) to implement the communication between the client and the server. The system consists of a daemon process working as a server and a set of client processes that provide different file and directory services. There may be running many different servers and clients over the same network. The client processes transparently locate the appropriate server for each transaction. The system also provides an open programming environment for the development of new applications. Both the user and the programmer interface of the system are kept close to standard UNIX.}, url = {http://cst.uop.gr/images/papers/1993-kassapidis-hci.pdf}, author = {Boucouvalas, C. and Costas Vassilakis and P. Georgiadis} } @conference {1993-vassilakis-hci, title = {A Methodology for the Implementation of Software for the Design of Distributed Systems}, booktitle = {Proceedings of the 4th Hellenic Conference on Informatics}, year = {1993}, month = {12}, pages = {673{\textendash}686}, abstract = {As the use of distributed systems is spreading, and applications designed for such systems become more and more demanding, optimal design of distributed systems becomes a critical issue. Designing a distributed system has become more complex, due to the number of alternatives for each decision that must be made and because of the existence of many parameters which influence the overal performance of the distributed system. Thus, it is necessary to use software tools, capable of accepting a description of the user{\textquoteright}s requirements and suggesting solutions to the problem of designing a distributed system which meets the user{\textquoteright}s requirements. In this paper, we present a disciplined approach to the construction of such a software tool, which combines methods from the Artificial Intelligence domain, that are used in order to design the distributed system, along with simulation techniques, used to estimate the system{\textquoteright}s overall performance.}, author = {Costas Vassilakis and P. Georgiadis and D. Lelis and D. Mouzakis and M. Nikolaidou} } @article {1993-spiliopoulou-cai, title = {Parallel Optimisation of Join Queries Using a Technique of Exhaustive Nature}, journal = {Computers and Artificial Intelligence}, volume = {12}, number = {2}, year = {1993}, pages = {145{\textendash}166}, abstract = {In this study we present a technique for the parallel optimisation of join queries that uses the offered coarse-grain parallelism of the underlying architecture in order to reduce the CPU-bound optimisation overhead. The optimisation technique performs an almost exhaustive search of the solution space for small join queries and gradually, as the number of joins increases, it diverges towards iterative improvement. This technique has been developed on a low-parallelism transputer-based architecture, where its behaviour is studied for the optimisation of queries with many tens of joins.}, keywords = {databases}, author = {M. Spiliopoulou and M. Hatzopoulos and Costas Vassilakis} } @conference {1992-spiliopoulou-parle, title = {Using Parallelism and Pipeline for the Optimisation of Join Queries}, booktitle = {PARLE {\textquoteright}92: Proceedings of the 4th International PARLE Conference on Parallel Architectures and Languages Europe}, year = {1992}, month = {6}, pages = {279{\textendash}294}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {In this study we present a technique for the parallel optimisation of join queries, that uses the offered coarse-grain parallelism of the underlying architecture in order to reduce the CPU-bound optimisation overhead. The optimisation technique performs an almost exhaustive search of the solution space for small join queries and gradually, as the number of joins increases, it diverges towards iterative improvement. This technique has been developed on a low-parallelism transputer-based architecture, where its behaviour is studied for the optimisation of queries with many tenths of joins.}, isbn = {3-540-55599-4}, doi = {10.1007/3-540-55599-4_94}, author = {M. Spiliopoulou and M. Hatzopoulos and Costas Vassilakis} } @conference {1990-hatzopoulos-delta, title = {An Object-Oriented Data Model for Hypermedia Systems}, booktitle = {Proceedings of the DELTA Conference in Research and Development}, year = {1990}, month = {10}, pages = {483{\textendash}493}, abstract = {Hypermedia [1] is a fast growing field of research interest because of the new aspects introduced as far as it concerns the interaction between the machine and the user. The innovative features mainly refer to - the presence of various information types (multimedia environment) - the mapping of the semantic connections between information items into a flexible, efficient representation. This feature enables navigation through the information network in a meaningful way. Our effort concentrated on the definition and partial implementation of a flexible, general-purpose model through which the full capabilities of object-oriented programming can be exploited.}, keywords = {databases}, url = {http://cst.uop.gr/images/papers/1990-hatzopoulos-delta.pdf}, author = {M. Hatzopoulos and D. Gouscos and M. Spiliopoulou and Costas Vassilakis and M. Vazirgiannis} }