@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 {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 {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 {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 Vasilakis} } @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 Vassilakis, Costas} } @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 = {Margaris, Dionisis and Spiliotopoulos, Dimitris and Karagiorgos, Gregory and Vassilakis, Costas 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} } @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 Vassilakis, Costas and Wallace, Manolis and Lantzouni, Marina and Poulopoulos, Vassilis and Margaris, Dionisis} } @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 Vassilakis, Costas 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 = {Margaris, Dionisis and Spiliotopoulos, Dimitris and Vasilopoulos, Dionysios and Vassilakis, Costas} } @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 C. Vassilakis and V. Poulopoulos} } @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 Vassilakis, Costas and Margaris, Dionisis} } @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 Vassilakis, Costas}, 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 {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 {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 {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} } @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 {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 = {Margaris, Dionisis and Vassilakis, Costas 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 {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 {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} } @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 {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} } @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} } @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 {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 {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} } @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 {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} } @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} } @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} } @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} } @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} } @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} } @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} } @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} } @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} } @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 {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 {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 {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} } @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} } @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} } @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 {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 {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 {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} } @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 {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} } @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} } @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 {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} } @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} } @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} } @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} } @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} } @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} } @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} } @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} } @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 {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} } @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} } @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 {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 {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 {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} } @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 {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} } @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} } @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} } @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} } @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} } @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 {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 {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} } @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/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} } @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} } @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} } @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 {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} } @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 {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} } @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} } @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} } @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} } @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} } @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} } @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} }