@article {831, title = {Blockchain meets Internet of Things (IoT) forensics: A unified framework for IoT ecosystems}, journal = {Internet of Things}, year = {2023}, month = {oct}, pages = {100968}, abstract = {

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

}, keywords = {blockchain, cyber-security, Digital forensics, Edge computing, Internet of Things}, doi = {10.1016/j.iot.2023.100968}, url = {https://www.sciencedirect.com/science/article/pii/S2542660523002913}, author = {Sotirios Brotsis and Konstantinos P. Grammatikakis and Dimitrios Kavallieros and Antonio I. Mazilu and Nicholas Kolokotronis and Konstantinos Limniotis and Costas Vassilakis} } @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} } @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} } @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 {783, title = {Threat landscape for smart grid systems}, booktitle = {Proceedings of the 15th International Conference on Availability, Reliability and Security}, year = {2020}, month = {jul}, publisher = {ACM}, organization = {ACM}, abstract = {

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

}, keywords = {attack detection features, attack mitigation, attacks, security, Smart grids}, doi = {https://doi.org/10.1145/3407023.3409229}, author = {Christos-Minas Mathas and Konstantinos-Panagiotis Grammatikakis and Costas Vassilakis and Nicholas Kolokotronis and Vasiliki-Georgia Bilali and Dimitris Kavallieros} } @conference {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} } @proceedings {DBLP:conf/pakdd/2018-2, title = {Advances in Knowledge Discovery and Data Mining - 22nd Pacific-Asia Conference, PAKDD 2018, Melbourne, VIC, Australia, June 3-6, 2018, Proceedings, Part II}, volume = {10938}, year = {2018}, publisher = {Springer}, isbn = {978-3-319-93036-7}, doi = {10.1007/978-3-319-93037-4}, url = {https://doi.org/10.1007/978-3-319-93037-4}, editor = {Dinh Q. Phung and Vincent S. Tseng and Geoffrey I. Webb and Bao Ho and Mohadeseh Ganji and Lida Rashidi} } @proceedings {DBLP:conf/gis/2018, title = {Proceedings of the 26th ACM SIGSPATIAL International Conference on Advances in Geographic Information Systems, SIGSPATIAL 2018, Seattle, WA, USA, November 06-09, 2018}, year = {2018}, publisher = {ACM}, isbn = {978-1-4503-5889-7}, url = {http://dl.acm.org/citation.cfm?id=3274895}, editor = {Farnoush Banaei Kashani and Erik G. Hoel and Ralf Hartmut G{\"u}ting and Roberto Tamassia and Li Xiong} } @proceedings {DBLP:conf/ssdbm/2018, title = {Proceedings of the 30th International Conference on Scientific and Statistical Database Management, SSDBM 2018, Bozen-Bolzano, Italy, July 09-11, 2018}, year = {2018}, publisher = {ACM}, doi = {10.1145/3221269}, url = {https://doi.org/10.1145/3221269}, editor = {Dimitris Sacharidis and Johann Gamper and Michael H. B{\"o}hlen} } @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} } @inbook {marg16d, title = {Knowledge-Based Leisure Time Recommendations in Social Networks}, booktitle = {Current Trends on Knowledge-Based Systems}, series = {Intelligent Systems Reference Library}, year = {2017}, pages = {23{\textendash}48}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, chapter = {Knowledge-Based Leisure Time Recommendations in Social Networks}, abstract = {We introduce a novel knowledge-based recommendation algorithm for leisure time information to be used in social networks, which enhances the state-of-the-art in this algorithm category by taking into account (a) qualitative aspects of the recommended places (restaurants, museums, tourist attractions etc.), such as price, service and atmosphere, (b) influencing factors between social network users, (c) the semantic and geographical distance between locations and (d) the semantic categorization of the places to be recommended. The combination of these features leads to more accurate and better user-targeted leisure time recommendations.}, keywords = {Attribute constraints, collaborative filtering, Knowledge-based Recommender Systems, Semantic Information, Social Networks}, doi = {10.1007/978-3-319-51905-0_2}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis}, editor = {Giner Alor Hernandez and Rafael Valencia Garcia} } @article {marg2017a-fgcs, title = {Query personalization using social network information and collaborative filtering techniques}, journal = {Future Generation of Computer Systems}, volume = {Special Issue on Recommender Systems for Large-Scale Social Networks}, year = {2017}, month = {jan}, pages = {440{\textendash}450}, abstract = {Query personalization has emerged as a means to handle the issue of information volume growth, aiming to tailor query answer results to match the goals and interests of each user. Query personalization dynamically enhances queries, based on information regarding user preferences or other contextual information; typically enhancements relate to incorporation of conditions that filter out results that are deemed of low value to the user and/or ordering results so that data of high value are presented first. In the domain of personalization, social network information can prove valuable; users{\textquoteright} social networks profiles, including their interests, influence from social friends, etc. can be exploited to personalize queries. In this paper, we present a query personalization algorithm, which employs collaborative filtering techniques and takes into account influence factors between social network users, leading to personalized results that are better-targeted to the user.}, doi = {10.1016/j.future.2017.03.015}, url = {http://www.sciencedirect.com/science/article/pii/S0167739X17303692}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @conference {margaris2016a, title = {Improving QoS Delivered by WS-BPEL Scenario Adaptation through Service Execution Parallelization}, booktitle = {Proceedings of the 31st Annual ACM Symposium on Applied Computing}, year = {2016}, pages = {1590-1596}, publisher = {ACM}, organization = {ACM}, abstract = {WS-BPEL scenario execution adaptation has been proposed by researchers as a response to the need of users to tailor the WS-BPEL scenario execution to their individual preferences; these preferences are typically expressed through Quality of Service (QoS) policies, which the adaptation mechanism considers in order to select the services that will ultimately be invoked to realize the desired business process. In this paper, we study the potential to parallelize the execution of the WS-BPEL scenario in order to minimize its response time and/or achieving higher scores in the other qualitative dimensions, such as cost, reliability, etc., at the same time. We also describe, develop and validate a parallelization algorithm for realizing the proposed enhancements.}, doi = {10.1145/2851613.2851805}, url = {https://dl.acm.org/citation.cfm?id=2851805}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @article {Margaris_2016, title = {Recommendation information diffusion in social networks considering user influence and semantics}, journal = {Social Network Analysis and Mining}, volume = {6}, number = {1}, year = {2016}, month = {nov}, pages = {108}, publisher = {Springer Nature}, abstract = {One of the major problems in the domain of social networks is the handling and diffusion of the vast, dynamic and disparate information created by its users. In this context, the information contributed by users can be exploited to generate recommendations for other users. Relevant recommender systems take into account static data from users{\textquoteright} profiles, such as location, age or gender, complemented with dynamic aspects stemming from the user behavior and/or social network state such as user preferences, items{\textquoteright} general acceptance and influence from social friends. In this paper, we enhance recommendation algorithms used in social networks by taking into account qualitative aspects of the recommended items, such as price and reliability, the influencing factors between social network users, the social network user behavior regarding their purchases in different item categories and the semantic categorization of the products to be recommended. The inclusion of these aspects leads to more accurate recommendations and diffusion of better user-targeted information. This allows for better exploitation of the limited recommendation space, and therefore online advertisement efficiency is raised.}, keywords = {Collaborative filtering, Information diffusion, Quality of service, Semantic Information, Social Networks}, doi = {10.1007/s13278-016-0416-z}, url = {http://rdcu.be/mZ7e}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @conference {575, title = {R-Susceptibility: An IR-Centric Approach to Assessing Privacy Risks for Users in Online Communities}, booktitle = {Proceedings of the 39th Annual International ACM SIGIR Conference}, year = {2016}, month = {July}, address = {Pisa, Italy}, author = {Joanna Asia Biega and Krishna P. Gummadi and Ida Mele and Dragan Milchevski and Christos Tryfonopoulos and Gerhard Weikum} } @proceedings {DBLP:conf/esws/2016, title = {The Semantic Web. Latest Advances and New Domains - 13th International Conference, ESWC 2016, Heraklion, Crete, Greece, May 29 - June 2, 2016, Proceedings}, volume = {9678}, year = {2016}, publisher = {Springer}, isbn = {978-3-319-34128-6}, doi = {10.1007/978-3-319-34129-3}, url = {https://doi.org/10.1007/978-3-319-34129-3}, editor = {Harald Sack and Eva Blomqvist and Mathieu d{\textquoteright}Aquin and Chiara Ghidini and Simone Paolo Ponzetto and Christoph Lange} } @conference {marg15a, title = {A Collaborative Filtering Algorithm with Clustering for Personalized Web Service Selection in Business Processes}, booktitle = {Proceedings of RCIS 2015}, year = {2015}, month = {5}, abstract = {Recommender systems aim to propose items that are expected to be of interest to the users. As one of the most successful approaches to building recommender systems, collaborative filtering exploits the known preferences of a group of users to formulate recommendations or predictions of the unknown preferences for other users. In many cases, collaborative filtering algorithms handle complex items, which are described using hierarchical tree structures containing rich semantic information. In order to make accurate recommendations on such items, the related algorithms must examine all aspects of the available semantic information. Thus, when collaborative filtering techniques are employed to adapt the execution of business processes, they must take into account the services{\textquoteright} Quality of Service parameters, so as to generate recommendations tailored to the individual user needs. In this paper, we present a collaborative filtering-based algorithm which takes into account the web services{\textquoteright} QoS parameters in order to tailor the execution of business processes to the preferences of users. An offline clustering technique is also introduced for supporting the efficient and scalable execution of proposed algorithm under the presence of large repositories of sparse data.}, keywords = {business processes, clustering, collaborative filtering, hierarchical tree, performance, Quality of service, Web services}, doi = {10.1109/RCIS.2015.7128877}, author = {Dionisis Margaris and P. Georgiadis and Costas Vassilakis} } @conference {margaris2015a, title = {A Hybrid Framework for WS-BPEL Scenario Execution Adaptation, Using Monitoring and Feedback Data}, booktitle = {Proceedings of the 30th ACM/SIGAPP Symposium On Applied Computing, SOAP track}, year = {2015}, month = {4}, publisher = {ACM}, organization = {ACM}, abstract = {In this paper, we present a framework which provides runtime adaptation for BPEL scenarios. The adaptation is based on (a) quality of service parameters of available web services (b) quality of service policies specified by users (c) collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, (d) monitoring, in order to follow the variations of QoS attribute values and (e) on users{\textquoteright} opinions services they have used.}, doi = {10.1145/2695664.2695687}, url = {https://dl.acm.org/citation.cfm?doid=2695664.2695687}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @article {margaris14a, title = {An integrated framework for adapting WS-BPEL scenario execution using QoS and collaborative filtering techniques}, journal = {Science of Computer Programming}, volume = {98}, year = {2015}, pages = {707{\textendash}734}, abstract = {In this paper, we present a framework which incorporates runtime adaptation for BPEL scenarios. The adaptation is based on (a) the quality of service parameters of available services, allowing for tailoring their execution to the diverse needs of individual users and (b)collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, in the context of the same business processes. The proposed framework also caters maintaining the transactional semantics that invocations to multiple services offered by the same provider may bear.}, doi = {10.1016/j.scico.2014.10.007}, url = {http://www.sciencedirect.com/science/article/pii/S0167642314004778}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @book {DBLP:books/sp/GL2015, title = {Medical Data Privacy Handbook}, year = {2015}, publisher = {Springer}, organization = {Springer}, isbn = {978-3-319-23632-2}, doi = {10.1007/978-3-319-23633-9}, url = {https://doi.org/10.1007/978-3-319-23633-9}, editor = {Aris Gkoulalas-Divanis and Grigorios Loukides} } @proceedings {DBLP:conf/kcap/2015, title = {Proceedings of the 8th International Conference on Knowledge Capture, K-CAP 2015, Palisades, NY, USA, October 7-10, 2015}, year = {2015}, publisher = {ACM}, isbn = {978-1-4503-3849-3}, doi = {10.1145/2815833}, url = {https://doi.org/10.1145/2815833}, editor = {Ken Barker and Jos{\'e} Manu{\'e}l G{\'o}mez-P{\'e}rez} } @conference {aamas15-GPT, title = {PViz: Visualising P2P Multi-Agent Simulations}, booktitle = {Proceedings of the International Conference on Autonomous Agents and Multiagent Systems (AAMAS)}, year = {2015}, month = {May}, pages = {1945{\textendash}1946}, address = {Istanbul, Turkey}, author = {Dimitris Giouroukis and Nikos Platis and Christos Tryfonopoulos} } @conference {margaris15c, title = {On Replacement Service Selection in WS-BPEL Scenario Adaptation}, booktitle = {Proceedings of the 8th IEEE International Conference on Service Oriented Computing \& Applications (SOCA 2015)}, year = {2015}, month = {9}, publisher = {IEEE}, organization = {IEEE}, abstract = {WS-BPEL scenario execution adaptation has been proposed by numerous researchers as a response to the need of users to tailor the WS-BPEL scenario execution to their individual preferences; these preferences are typically expressed through Quality of Service (QoS) policies, which the adaptation mechanism considers in order to select the services that will ultimately be invoked to realize the desired business process. In this paper, we consider a number of issues related to WS-BPEL scenario adaptation, aiming to enhance adaptation quality and improve the QoS offered to end users. More specifically, with the goal of broadening the service selection pool we (a) discuss the identification of potential services that can be used to realize a functionality used in the WS-BPEL scenario and (b) elaborate on transactional semantics that invocations to multiple services offered by the same provider may bear. We also describe and validate an architecture for realizing the proposed enhancements.}, doi = {10.1109/SOCA.2015.11}, author = {Dionisis Margaris and P. Georgiadis and Costas Vassilakis} } @inbook {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} } @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} } @proceedings {DBLP:conf/edbt/2014, title = {Proceedings of the 17th International Conference on Extending Database Technology, EDBT 2014, Athens, Greece, March 24-28, 2014}, year = {2014}, publisher = {OpenProceedings.org}, url = {http://openproceedings.org/html/pages/2014_edbt.html}, editor = {Sihem Amer-Yahia and Vassilis Christophides and Anastasios Kementsietsidis and Minos N. Garofalakis and Stratos Idreos and Vincent Leroy} } @conference {DBLP:conf/edbt/PoulisGLST14, title = {SECRETA: A System for Evaluating and Comparing RElational and Transaction Anonymization algorithms}, booktitle = {Proceedings of the 17th International Conference on Extending Database Technology, EDBT 2014, Athens, Greece}, year = {2014}, month = {March 24-28}, pages = {620{\textendash}623}, doi = {10.5441/002/edbt.2014.58}, url = {https://doi.org/10.5441/002/edbt.2014.58}, author = {Giorgos Poulis and Aris Gkoulalas-Divanis and Grigorios Loukides and Spiros Skiadopoulos and Christos Tryfonopoulos} } @conference {Margaris2013RCIS, title = {Adapting WS-BPEL scenario execution using collaborative filtering techniques}, booktitle = {IEEE 7th International Conference on Research Challenges in Information Science (RCIS)}, year = {2013}, month = {may}, publisher = {IEEE}, organization = {IEEE}, abstract = {WS-BPEL has been adopted as the predominant method for composing individual web services into higher-level business processes. The designers of WS-BPEL scenarios define at development time the specific web services that will be invoked in the context of the business process they model; in the context however of the current web, where each functionality is offered by multiple service providers, under different quality of service parameters, using a fixed BPEL scenario has been recognized to be inadequate for servicing the diverse needs of business processes clients. To this end, WS-BPEL scenario execution adaptation has been proposed, mainly allowing clients to specify quality of service policies, which drive the dynamic selection of the services that will be invoked. In this paper, we present a framework extending the quality of service-based adaptation mechanisms with collaborative filtering techniques, allowing clients to further refine the adaptation process by considering service selections made by other clients, in the context of the same business processes.}, doi = {10.1109/rcis.2013.6577691}, author = {Dionisis Margaris and P. Georgiadis and Costas Vassilakis} } @conference {DBLP:conf/pkdd/PoulisLGS13, title = {Anonymizing Data with Relational and Transaction Attributes}, booktitle = {Machine Learning and Knowledge Discovery in Databases - European Conference, ECML PKDD 2013, Prague, Czech Republic, September 23-27, 2013, Proceedings, Part III}, year = {2013}, pages = {353{\textendash}369}, doi = {10.1007/978-3-642-40994-3_23}, url = {https://doi.org/10.1007/978-3-642-40994-3_23}, author = {Giorgos Poulis and Grigorios Loukides and Aris Gkoulalas-Divanis and Spiros Skiadopoulos} } @conference {DBLP:conf/mdm/PoulisSLG13, title = {Distance-Based k\^m-Anonymization of Trajectory Data}, booktitle = {2013 IEEE 14th International Conference on Mobile Data Management, Milan, Italy, June 3-6, 2013 - Volume 2}, year = {2013}, pages = {57{\textendash}62}, doi = {10.1109/MDM.2013.66}, url = {https://doi.org/10.1109/MDM.2013.66}, author = {Giorgos Poulis and Spiros Skiadopoulos and Grigorios Loukides and Aris Gkoulalas-Divanis} } @conference {Margaris2013SAC, title = {An integrated framework for QoS-based adaptation and exception resolution in WS-BPEL scenarios}, booktitle = {Proceedings of the 28th Annual ACM Symposium on Applied Computing - SAC \textquotesingle13}, year = {2013}, month = {3}, publisher = {ACM Press}, organization = {ACM Press}, abstract = {In this paper, we present a framework which incorporates runtime quality of service-based adaptation for BPEL scenarios, allowing for tailoring their execution to the diverse needs of individual users. The proposed framework also caters for automatically resolving system-level exceptions, such as machine outages or network partitionings, while both scenario execution adaptation and exception resolution maintain the transactional semantics that invocations to multiple services offered by the same provider may bear.}, doi = {10.1145/2480362.2480714}, author = {Dionisis Margaris and Costas Vassilakis and P. Georgiadis} } @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 {Giannikopoulos2011, title = {A distributed recommender system architecture}, journal = {International Journal of Web Engineering and Technology}, volume = {7}, number = {3}, year = {2012}, pages = {203{\textendash}227}, abstract = {In contemporary internet architectures, including server farms and blog aggregators, web log data may be scattered among multiple cooperating peers. In order to perform content personalization through provision of recommendations on such architectures, it is necessary to employ a recommendation algorithm; however the majority of such algorithms are centralized, necessitating excessive data transfers and exhibiting performance issues when the number of users or the volume of data increase. In this paper we propose an approach where the clickstream information is distributed to a number of peers, which cooperate for discovering frequent patterns and for generating recommendations, introducing (a) architectures that allow the distribution of both the content and the clickstream database to the participating peers and (b) algorithms that allow collaborative decisions on the recommendations to the users, in the presence of scattered log information. The proposed approach may be employed in various domains, including digital libraries, social data, server farms and content distribution networks.}, doi = {10.1504/IJWET.2012.048517}, author = {Giannikopoulos, P. and Costas Vassilakis} } @article {vassiliadis2010c, title = {Modelling and performance evaluation of a novel internal priority routing scheme for finite-buffered multistage interconnection networks}, journal = {International Journal of Parallel, Emergent and Distributed Systems}, volume = {26(5)}, year = {2011}, pages = {381{\textendash}397}, abstract = {In this paper, the modelling, analysis and performance evaluation of a novel architecture for internal priority finite-buffered Multistage Interconnection Networks (MINs) is presented. We model the proposed architecture giving the details of its operation and describing its states and detailing conditions and effects of state transition; we also provide a formal model for evaluating its performance. The proposed architecture{\textquoteright}s performance is subsequently analyzed under the uniform traffic condition, considering various offered loads, buffer-lengths and MIN sizes, using simulations. We compare the internal priority scheme vs. the non priority (or single priority) scheme, by gathering metrics for the two most important network performance factors, namely packet throughput and the mean time a packet needs to traverse the network. We demonstrate and quantify the improvements on MIN performance stemming from the introduction of priorities in terms of throughput and a combined performance indicator which depicts the overall performance of the MIN. These performance measures can be valuable assets for designers of parallel multiprocessor systems and networks in order to minimize the overall deployment costs and delivering efficient systems.}, doi = {10.1080/17445760.2010.539218}, url = {https://www.tandfonline.com/doi/abs/10.1080/17445760.2010.539218}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis and E. Glavas} } @article {Kareliotis2009284, title = {IQoS-aware exception resolution for BPEL processes: A middleware-based framework and performance evaluation}, journal = {International Journal of Web and Grid Services}, volume = {5}, number = {3}, year = {2009}, note = {cited By (since 1996) 0}, pages = {284-320}, abstract = {Web Services Business Process Execution Language (WS-BPEL) is widely used nowadays for specifying and executing composite business processes. During the execution, however, of such business processes, a number of faults stemming from the nature of SOA may occur. The WS-BPEL scenario designer must therefore use the provisions offered by WS-BPEL to catch these exceptions and resolve them. The system fault handler specification, however, is an additional task for the WS scenario designer, while the presence of such handlers within the scenario necessitates extra maintenance activities. In this paper, we propose a middleware-based framework for system exception resolution, which undertakes the tasks of failure interception, discovery of alternative services and their invocation. The process of selecting the alternative services can be driven by process consumer-specified Quality of Service (QoS) policy. Moreover, the middleware arranges for bridging syntactic differences between the originally invoked services and functionally equivalent replacements to it, by employing XSLT-based transformations. The middleware is deployed and maintained independently of the WS-BPEL scenarios, thus removing the need for specifying and maintaining system fault handlers within the scenarios. We also present performance measures, establishing that the overhead imposed by the addition of the proposed middleware layer is minimal. Copyright Β{\textcopyright} 2009, Inderscience Publishers.}, keywords = {Ad hoc networks, BPEL process, Exception handling, Exception resolution, Middleware, Performance metrics, QoS, Quality control, Quality of service, Scalability, Telecommunication services, Web services}, doi = {10.1504/IJWGS.2009.028346}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70349462474\&partnerID=40\&md5=4511b42fde076617cd6ac0139e3f588d}, author = {Christos Kareliotis and Costas Vassilakis and S. Rouvas and P. Georgiadis} } @conference {Vasiliadis2009395, title = {Performance evaluation of multicast routing over multilayer multistage interconnection networks}, booktitle = {Proceedings of the 2009 5th Advanced International Conference on Telecommunications, AICT 2009}, year = {2009}, note = {cited By (since 1996) 0}, month = {5}, pages = {395-403}, abstract = {Multilayer MINs have emerged mainly due to the increased need for routing capacity in the presence of multicast and broadcast traffic, their performance prediction and evaluation however has not been studied sufficiently insofar. In this paper, we use simulation to evaluate the performance of multilayer MINs with switching elements of different buffer sizes and under different offered loads. The findings of this paper can be used by MIN designers to optimally configure their networks. Β{\textcopyright} 2009 IEEE.}, keywords = {Broadcast traffic, Buffer sizes, Interconnection networks, Multicast routing, Multicasting, Multicasts, Multilayers, Multistage interconnection network, Network routing, Performance evaluation, Performance prediction, Switching elements}, doi = {10.1109/AICT.2009.72}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70349732883\&partnerID=40\&md5=e85525a7b36de8d84ea1ae52110ff1f9}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis and E. Glavas} } @conference {Christos2009271, title = {QoS-driven adaptation of BPEL scenario execution}, booktitle = {2009 IEEE International Conference on Web Services, ICWS 2009}, year = {2009}, note = {cited By (since 1996) 0}, month = {7}, pages = {271-278}, abstract = {BPEL/WSBPEL is the predominant approach for combining individual web services into integrated business processes, allowing for the specification of their sequence, control flow and data exchanges. BPEL however does not include mechanisms for considering the invoked services{\textquoteright} Quality of Service (QoS) parameters and thus BPEL scenarios can neither tailor their execution to the individual user{\textquoteright}s needs or adapt to the highly dynamic environment of the WEB, where new services may be deployed, old ones withdrawn or existing ones changing their QoS parameters. Moreover, infrastructure failures in the distributed environment of the web introduce an additional source of failures that must be considered in the context of QoS-aware service execution. In this work we propose a framework for addressing the issues identified above; the framework allows the users to specify the QoS parameters that they require and it undertakes the task of locating and invoking suitable services. Finally, the proposed framework intercepts and resolves faults occurring during service invocation, respecting the QoS restrictions specified by the consumer. Β{\textcopyright} 2009 IEEE.}, keywords = {Adaptive execution, BPEL, Control flows, Data exchange, Distributed environments, Dynamic environments, Infrastructure failures, Integrated business, New services, Performance evaliation, QoS parameters, Quality of service, Quality of Service parameters, Service execution, Service invocation, Web services}, doi = {10.1109/ICWS.2009.80}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70449472686\&partnerID=40\&md5=5303ebeff04a4e7a062f77209521d561}, author = {Christos Kareliotis and Costas Vassilakis and S. Rouvas and P. Georgiadis} } @conference {golem2009b, title = {Visualizing Hierarchies: Evaluating the Efficiency and Cognitive Effects of Six Visualization Techniques for Browsing and Management Tasks}, booktitle = {Information Visualization 2009, book of abstracts}, year = {2009}, month = {7}, abstract = {Hierarchical data structures are one of the most commonly used data structures in computer science, and therefore numerous methods and techniques have been proposed for their visualization. In this paper, we present our findings from a user study, in which a number of folder visualization environments were evaluated to assess (a) how efficiently a number of tasks can be performed within the different environments (b) the extent to which using a particular visualization may help the user acquire an accurate cognitive image of the hierarchy structure and its contents and (c) the overall user experience from using a particular visualization environment. The visualization environments considered are representative of major visualization paradigms (zoomable user interfaces, context+focus and space-filling), while both 2D and 3D environments have been included.}, author = {M. Golemati and Costas Vassilakis and Akrivi Katifori and Giorgos Lepouras and C. Halatsis} } @conference {Christos2008248, title = {Exception resolution for BPEL processes: A middleware-based framework and performance evaluation}, booktitle = {Proceedings of the 10th International Conference on Information Integration and Web-based Applications and Services, iiWAS 2008}, year = {2008}, note = {cited By (since 1996) 0}, month = {12}, pages = {248-256}, abstract = {WS-BPEL is widely used nowadays for specifying and executing composite business processes within the Service Oriented Architecture (SOA). During the execution however, of such business processes, a number of faults stemming from the nature of SOA (e.g. network or server failures) may occur. The WS-BPEL scenario designer must therefore use the provisions offered by WS-BPEL to catch these exceptions and resolve them, usually by invoking some equivalent web service that is expected to be reachable and available. System fault handler specification is though an additional task for the WS scenario designer, while the presence of such handlers within the scenario necessitates extra maintenance activities, as new alternate services emerge or some of the specified ones are withdrawn. In this paper, we propose a middleware-based framework for system exception resolution, which undertakes the tasks of failure interception, discovery of alternate services and their invocation. The middleware is deployed and maintained independently of the WS-BPEL scenarios, removing thus the need for specifying and maintaining system fault handlers within the scenarios. We also present performance measures, establishing that the overhead imposed by the addition of the proposed middleware layer is minimal. Β{\textcopyright} 2008 ACM.}, keywords = {Ad hoc networks, Business Process, Exception handling, Information retrieval, Information services, Maintenance activity, Middleware, Middleware layer, Performance evaluation, Performance measure, Performance metrics, Quality control, Quality of service, Quality of service (QoS), Scalability, Service oriented architecture (SOA), System faults, Telecommunication services, Web services, WS-BPEL}, doi = {10.1145/1497308.1497355}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-70349146138\&partnerID=40\&md5=9a5231fe52fffef11707efd4f3489a37}, author = {Christos Kareliotis and Costas Vassilakis and S. Rouvas and P. Georgiadis} } @inbook {gol2009a, title = {Intelligent User Interfaces: Adaptation and Personalization Systems and Technologies}, year = {2008}, pages = {188{\textendash}204}, publisher = {IGI Publishing}, organization = {IGI Publishing}, chapter = {Context and Adaptivity-Driven Visualization Method Selection}, abstract = {Novel and intelligent visualization methods are being developed in order to accommodate user searching and browsing tasks, including new and advanced functionalities. Besides, research in the field of user modeling is progressing in order to personalize these visualization systems, according to its users{\textquoteright} individual profiles. However, employing a single visualization system, may not suit best any information seeking activity. In this paper we present a visualization environment, which is based on a visualization library, i.e. is a set of visualization methods, from which the most appropriate one is selected for presenting information to the user. This selection is performed combining information extracted from the context of the user, the system configuration and the data collection. A set of rules inputs such information and assigns a score to all candidate visualization methods. The presented environment additionally monitors user behavior and preferences to adapt the visualization method selection criteria.}, author = {M. Golemati and Costas Vassilakis and Akrivi Katifori and Giorgos Lepouras and C. Halatsis}, editor = {C. Mourlas and P. Germanakos} } @conference {Golemati2008106, title = {An interview-based user study on the use of visualizations for folder browsing}, booktitle = {Proceedings of the International Conference on Information Visualisation}, year = {2008}, note = {cited By (since 1996) 0}, month = {7}, pages = {106-112}, abstract = {Hierarchically structured data collections often need to be visualized for the purposes of digital information management and presentation. File browsing, in particular, has an inherent hierarchical structure and plays an important role in the context of Personal Information Management (PIM). A multitude of file browsers are nowadays available, offering different functionalities, while users adopt diverse practices and habits for browsing activities. In this paper, we investigate these aspects to obtain insights into their advantages and disadvantages and suggest solutions in the area of PIM, as well as in other domains employing similar visualization paradigms. The presented study focuses on the two most widespread visualizations used by file browsers, the indented list and zoomable interface paradigms, and assesses their effectiveness for various tasks and contexts, both by exploiting results on existing evaluations on hierarchy visualizations and folder hierarchy visualizations in particular, and by conducting an interviewbased user study. Β{\textcopyright} 2008 IEEE.}, keywords = {Administrative data processing, File browser visualization, Indented list visualization, Information analysis, Information management, Information science, Intermodulation, Intermodulation measurement, International conferences, Management, Management information systems, Telecommunication services, User study, Windows explorer}, doi = {10.1109/IV.2008.90}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-51749097531\&partnerID=40\&md5=66afc30e74191773d1c950ac83ba9ac7}, author = {M. Golemati and Akrivi Katifori and E.G. Giannopoulou and I. Daradimos and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @conference {Vasiliadis200856, title = {Routing and performance analysis of double-buffered omega networks supporting multi-class priority traffic}, booktitle = {Proc. - The 3rd Int. Conf. Systems and Networks Communications, ICSNC 2008 - Includes I-CENTRIC 2008: Int. Conf. Advances in Human-Oriented and Personalized Mechanisms, Technologies, and Services}, year = {2008}, note = {cited By (since 1996) 1}, month = {10}, pages = {56-63}, abstract = {In this paper the modeling of Omega Networks supporting multi-class routing traffic is presented and their performance is analyzed. We compare the performance of multi-class priority mechanism against the single priority one, by gathering metrics for the two most important network performance factors, namely packet throughput and delay under uniform traffic conditions and various offered loads, using simulations. Moreover, two different test-bed setups were used in order to investigate and analyze the performance of all priority-class traffic, under different Quality of Service (QoS) configurations. In the considered environment, Switching Elements (SEs) that natively support multi-class priority routing traffic are used for constructing the MIN, while we also consider double-buffered SEs, two configuration parameters that have not been addressed insofar. The rationale behind introducing a multiple-priority scheme is to provide different QoS guarantees to traffic from different applications, which is a highly desired feature for many IP network operators, and particularly for enterprise networks. Β{\textcopyright} 2008 IEEE.}, keywords = {Computer networks, Configuration parameters, Enterprise networks, Ip networks, Metropolitan area networks, Network performances, Packet throughputs, Performance analyses, Priority schemes, Qos guarantees, Quality of service, Routing traffics, Set-ups, Systems engineering, Uniform traffics}, doi = {10.1109/ICSNC.2008.10}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-58149096344\&partnerID=40\&md5=11b2d45a47554d3556034866c2f3ac49}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis and E. Glavas} } @conference {kalikakis2007b, title = {An Approach for re-engineering the Taxation Process to Support Participatory Decisions on Tax Budget Allocation}, booktitle = {Proceedings of the 1st International Conference on Methodologies, Technologies and Tools enabling e-Government}, year = {2007}, month = {9}, abstract = {The tax collection process has been described as a bureaucratic one, that confines citizen involvement to the role of passive fulfillment of administrative and financial obligations. Active citizen participation, in the form of some political say on the allocation of collected taxes which could potentially improve and further legitimize tax collection, is not a part of the traditional taxation model. In this paper we describe a new taxation model which, in the spirit of participatory budgeting approaches, supports active citizens? participation on decision making regarding tax funds allocation.}, author = {M. Kalikakis and D. Gouscos and Costas Vassilakis and P. Georgiadis} } @conference {KatiforiGVLH07, title = {Creating an Ontology for the User Profile: Method and Applications}, booktitle = {RCIS}, year = {2007}, month = {4/2007}, pages = {407{\textendash}412}, abstract = {User profiling is commonly employed nowadays to enhance usability as well as to support personalization, adaptivity and other user-centric features. Insofar, application designers model user profiles mainly in an ad-hoc manner, hindering thus application interoperability at the user profile level, increasing the amount of work to be done and the possibility of errors or omissions in the profile model. This work aims at creating a user profile ontology that incorporates concepts and properties used to model the user profile. Existing literature, applications and ontologies related to the domain of user context and profiling have been taken into account in order to create a general, comprehensive and extensible user model. This ontology can be used as a reference model, in order to alleviate the aforementioned issues. The model, available for download, is exemplified through its application in two different areas, personal information management and adaptive visualization.}, author = {Akrivi Katifori and M. Golemati and Costas Vassilakis and Giorgos Lepouras and C. Halatsis} } @article {Lepouras200779, title = {Domain expert user development: The smartgov approach}, journal = {Communications of the ACM}, volume = {50}, number = {9}, year = {2007}, month = {sep}, pages = {79-83}, publisher = {Association for Computing Machinery (ACM)}, abstract = {SmartGov project funded by the European Union is a knowledge-based platform that assists pubic-sector employees with suitable expertise to generate online transaction devices by simplifying service development, maintenance, and integration with installed information technology systems. The project delivers intelligent e-forms development and maintenance environment and associated framework for e-government services. SmartGov address various problems faced by the stakeholders while implementing e-services such as limited view of domain experts, lost information, complexity of creating e-forms, and inadequate access. In a SmartGov approach, the implicit knowledge is made explicit in the form of documentation and data validation rules. The central concept of SmartGov is the transaction service element (TSE) that contain metadata and domain knowledge.}, keywords = {Data validation, Documentation, Information services, Information technology, Knowledge based platform, Knowledge based systems, Metadata, Online systems, Project management, Transaction service element (TSE)}, doi = {10.1145/1284621.1284623}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-34548411694\&partnerID=40\&md5=43df285b5a79ef731b3466106642af9f}, author = {Giorgos Lepouras and Costas Vassilakis and C. Halatsis and P. Georgiadis} } @conference {DBLP:conf/icws/KareliotisVG07, title = {Enhancing BPEL scenarios with Dynamic Relevance-Based Exception Handling}, booktitle = {ICWS}, year = {2007}, month = {7}, pages = {751-758}, abstract = {Web services have become the key technology in business processes management. Business processes can be self-contained or be composed from sub-processes; the latter category is typically specified using the Web Services Business Process Execution Language (WS-BPEL) and executed by a Web Services Orchestrator (WSO). During the execution however of such a composite service, a number of faults stemming from the distributed nature of the SOA architecture, e.g. network or server failures may occur. WS-BPEL includes provisions for exception handling, which can be exploited for detecting such failures; once detected, a failure can be resolved by invoking alternate web service implementations that perform the same business task as the failed one. However, the inclusion of such provisions is a tedious assignment for the business process designer, while additional effort would be required to maintain the BPEL scenarios in cases that some alternate WS implementations cease to exist or new ones are introduced. In our research we are developing a framework for automating handling of that kind of exceptions. The proposed solution employs a pre-processor that enhances BPEL scenarios with code that detects failures, discovers alternate WS implementations and invokes them, fully thus resolving the exception. Alternate WS implementation discovery is based on service relevance, which takes into account both functional and qualitative properties of web services.}, doi = {10.1109/ICWS.2007.86}, author = {Christos Kareliotis and Costas Vassilakis and P. Georgiadis} } @conference {Golemati200793, title = {Evaluating the significance of the windows explorer visualization in personal information management browsing tasks}, booktitle = {Proceedings of the International Conference on Information Visualisation}, year = {2007}, note = {cited By (since 1996) 0}, month = {7}, pages = {93-98}, abstract = {The visualization of hierarchies is very important for digital information management and presentation systems. Especially in the context of Personal Information Management, file browsers play a very important role. Currently the most common file browser visualizations are Windows Explorer and the simple zoomable visualization offered by Microsoft Windows. This work explores the issue of file browser visualization through a user study based on inter-views and an experiment. Β{\textcopyright} 2007 IEEE.}, keywords = {Data reduction, File browser visualization, Hierarchical systems, Indented list visualization, Information analysis, User study, Web browsers, Windows explorer}, doi = {10.1109/IV.2007.46}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-35348919670\&partnerID=40\&md5=f35f306d4063ee2e91e3c573f4ed5d8a}, author = {M. Golemati and Akrivi Katifori and E.G. Giannopoulou and I. Daradimos and Costas Vassilakis} } @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 {Katifori2007, title = {Ontology visualization methods - A survey}, journal = {ACM Computing Surveys}, volume = {39}, number = {4}, year = {2007}, note = {cited By (since 1996) 21}, pages = {10:1-10:43}, abstract = {Ontologies, as sets of concepts and their interrelations in a specific domain, have proven to be a useful tool in the areas of digital libraries, the semantic web, and personalized information management. As a result, there is a growing need for effective ontology visualization for design, management and browsing. There exist several ontology visualization methods and also a number of techniques used in other contexts that could be adapted for ontology representation. The purpose of this article is to present these techniques and categorize their characteristics and features in order to assist method selection and promote future research in the area of ontology visualization. Β{\textcopyright} 2007 ACM.}, keywords = {Digital libraries, Human computer interaction, Information management, Ontology, Ontology representation, Ontology visualization, Personalized information management, Semantic Web, visualization methods}, doi = {10.1145/1287620.1287621}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-36048959880\&partnerID=40\&md5=a74cd76829bee9bb1cc21d6118e65340}, author = {Akrivi Katifori and C. Halatsis and Giorgos Lepouras and Costas Vassilakis and E.G. Giannopoulou} } @conference {Vasiliadis2007a, title = {Performance evaluation of two-priority network schema for single-buffered delta networks}, booktitle = {IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC}, year = {2007}, note = {cited By (since 1996) 0}, month = {9}, abstract = {In this paper a novel two-priority network schema is presented, and exemplified through its application on singlebuffered Delta Networks in packet switching environments. Network operations considered include conflict resolution and communication strategies. The proposed scheme is evaluated and compared against the single-priority scheme. Performance evaluation was conducted through simulation, due to the complexity of the model, and uniform traffic conditions were considered. Metrics were gathered for the two most important network performance factors, namely packet throughput and the mean time a packet needs to traverse the network. The model can also be uniformly applied to several representative networks providing a basis for fair comparison and the necessary data for network designers to select optimal values for network operation parameters. Β{\textcopyright} 2007 IEEE.}, keywords = {Computer simulation, Mobile radio systems, Network operations, Packet switching, Single-buffered delta networks, Telecommunication networks, Telecommunication traffic}, doi = {10.1109/PIMRC.2007.4394153}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-44349140122\&partnerID=40\&md5=d8cd4384e09916ce753625ec5f2c8549}, author = {D.C. Vasiliadis and G.E. Rizos and Costas Vassilakis and E. Glavas} } @conference {DBLP:conf/www/GhinitaKS07, title = {PRIVE: anonymous location-based queries in distributed mobile systems}, booktitle = {Proceedings of the 16th International Conference on World Wide Web, WWW 2007, Banff, Alberta, Canada, May 8-12, 2007}, year = {2007}, pages = {371{\textendash}380}, doi = {10.1145/1242572.1242623}, url = {https://doi.org/10.1145/1242572.1242623}, author = {Gabriel Ghinita and Panos Kalnis and Spiros Skiadopoulos} } @conference {kalikakis2007a, title = {Towards a P2P world: peered taxation}, booktitle = {Proceedings of the 2nd International Workshop "E-taxation: State \& Perspectives"}, year = {2007}, month = {2}, abstract = {This paper presents the current model for taxation and distribution of the taxes to government activities, and an alternative model is presented, according to which tax-payers can determine, to some extent, the way that the taxes they pay will be spent. The goal of this proposal is to increase citizen involvment and system transparency. The model proposal comescomplete with an architecture that supports the realization of the proposed scheme}, author = {M. Kalikakis and D. Gouscos and Costas Vassilakis and P. Georgiadis} } @conference {Golemati200662, title = {A context-based adaptive visualization environment}, booktitle = {Proceedings of the International Conference on Information Visualisation}, year = {2006}, note = {cited By (since 1996) 0}, month = {7}, pages = {62-67}, abstract = {Digital libraries and historical archives are increasingly employing visualization systems to facilitate the information retrieval and knowledge extraction tasks of their users. Typically, each organization employs a single visualization system, which may not suit best the needs of certain user groups, specific tasks, or properties of document collections to be visualized. In this paper we present a context-based adaptive visualization environment, which embeds a set of visualization methods into a visualization library, from which the most appropriate one is selected for presenting information to the user. Methods are selected by examining parameters related to the user profile, system configuration and the set of data to be visualized, and employing a set of rules to assess the suitability of each method. The presented environment additionally monitors user behavior and preferences to adapt the visualization method selection criteria. Β{\textcopyright} 2006 IEEE.}, keywords = {(PL) properties, Adaptive systems, Adaptive visualization, Behavioral research, Digital libraries, document collections, Extraction, Information analysis, Information science, Information services, Information systems, Information visualization, Knowledge extraction, Libraries, Retrieval (MIR), Search engines, Selection criterion, Set of rules, Solvent extraction, Specific tasks, System configurations, User behaviors, User groups, user profiling, Visualization, visualization methods, Visualization systems}, doi = {10.1109/IV.2006.5}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-45149121827\&partnerID=40\&md5=ec45ad555b132faaf0bd2ca53e3292dc}, author = {M. Golemati and C. Halatsis and Costas Vassilakis and Akrivi Katifori and Giorgos Lepouras} } @conference {kareliotis2006, title = {Towards Dynamic, Relevance-Driven Exception Resolution in Composite Web Services}, booktitle = {Proceedings of OOPSLA 2006, Fourth International Workshop on SOA \& Web Services Best Practices}, year = {2006}, month = {10}, abstract = {Web services have become the leading technology for application-toapplication (A2A) communication over distributed and heterogeneous environments. Both academia and industry have strived to enable useful service collaborations among distributed systems without any human intervention. Web service composition can be used to this end, to achieve business automation within one company or realize business-to-business (B2B) integration of heterogeneous software and cross-organizational computing systems. Service composition pro-vides added value, when a web service composition itself becomes a higher level composite web service. However, as business processes are long-lasting transactions, exceptions may often occur, necessitating the replacement of a service component which has been made unavailable, hindering the completion of some business process. In this paper we present an exception resolving approach based on discovering replacement components that are functionally equivalent, taking also into account criteria for qualitative substitutability. The proposed solution introduces the Service Relevance and Replacement Framework (SRRF) which undertakes exception handling.}, author = {Christos Kareliotis and Costas Vassilakis and P. Georgiadis} } @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} } @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 {Vassilakis200581, title = {Exploiting form semantics and validation checks to improve e-form layout}, journal = {International Journal of Web Engineering and Technology}, volume = {2}, number = {1}, year = {2005}, note = {cited By (since 1996) 0}, pages = {81-96}, abstract = {On their route to the electronic era, organisations release on the web more and more complex form-based services, which require users to enter numerous data items interrelated by business rules. In such a context, it is crucial to provide optimal form layouts, in order to present the service users with interfaces that facilitate their work. This paper presents an integrated environment, which exploits data item interrelations manifested by the business rules (or validation checks), to optimise the layout of the web forms comprising a complex service. The approach is validated through its application on a tax return form e-service. Copyright Β{\textcopyright} 2005 Inderscience Enterprises Ltd.}, keywords = {electronic services, Form layout, Form semantics, Integrated environment, Interfaces (computer), Optimization, semantics, Taxation, Usuability, Validation checks, World Wide Web}, doi = {10.1504/IJWET.2005.007465}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-24344507764\&partnerID=40\&md5=e94b487785303410cb7bf88df9d12c86}, author = {Costas Vassilakis and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @article {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 {Vassilakis2005421, title = {A semantics-based consultations workbench}, booktitle = {ITI 3rd International Conference on Information and Communications Technology, ICICT 2005 - Enabling Technologies for the New Knowledge Society}, volume = {2005}, year = {2005}, note = {cited By (since 1996) 0}, month = {12}, pages = {421-434}, abstract = {Econsultations constitute an effective means to inclusive and informed participation of citizens and society in policy, decision and law formulation processes, and an answer to democratic deficit issues. Econsultation platforms need to support all stages of consultation processes including agenda setting and topics raising, legislation proposal publicity, notification of developments, proposal debate and commentary, collection, analysis and synthesis of views. In this paper we present the design of an open platform assisting policy makers and the civil society in the set-up, enactment, management and federation of inclusive and informed digital consultations. The proposed platform employs semantic techniques, such as semantics, content annotation and summarization to support the consultation processes and provide targeted and digested information to participants, and facilitates tailoring of Econsultation procedures by offering basic Econsultation activities as building blocks, which can be combined according to contextual needs. The platform also enables distinct Econsultation processes to be federated, allowing the exchange of information, which may be subject to different semantic annotations and classifications, according to the rules of each Econsultation process.}, keywords = {Classification (of information), Content annotation, Data transfer, Decision making, Econsultations, Knowledge based systems, Logic programming, Platform architecture, Public policy, Semantic technologies, semantics}, doi = {10.1109/ITICT.2005.1609641}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-33847729948\&partnerID=40\&md5=54c7a246c0ee9ae483889741a327253b}, author = {Costas Vassilakis and D. Gouscos and P. Georgiadis} } @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} } @article {DBLP:journals/eg/VassilakisLRG04, title = {Integrating e-government public transactional services into public authority workflows}, journal = {Electronic Government}, volume = {1}, number = {1}, year = {2004}, pages = {49-60}, abstract = {Documents submitted by citizens through electronic services deployed in the context of e-Government must usually undergo processing by some organisational information system, in order to complete the citizens? requests and for the reply to be returned to the citizen. The integration, however, of the e-service delivery platform and the organisational information system is often hindered for a number of reasons, including security considerations, platform diversity or idiosyncrasies of legacy information systems. In this paper we present a generic method for providing seamless communication between the two platforms, enabling the full integration of documents submitted through electronic services into the organisational workflow, leveraging thus the quality of services offered to the citizens and facilitating e-service development and operation.}, doi = {10.1504/EG.2004.004136}, author = {Costas Vassilakis and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @article {Maroulis2004267, title = {A web browser for ISDN card phones}, journal = {Journal of Internet Technology}, volume = {5}, number = {3}, year = {2004}, note = {cited By (since 1996) 1}, pages = {267-277}, abstract = {In order to cover the ever-increasing need for more direct and easy access to information, new information access means need to be devised or existing ones need to be further exploited. In this paper, we present a mini Web Browser for ISDN card phones, which enables this widespread device to be used for accessing information in the World Wide Web. The implemented web browser supports HTML and WML pages, while special care was taken to tackle the limitations imposed by the ISDN card phone{\textquoteright}s hardware, such as small screen, limited keyboard, scarce processing and memory resources. One of the techniques employed to increase the capabilities of the ISDN card phone browser was the introduction of a proxy server, which transforms demanding media types to formats that can be handled by the ISDN card phone hardware.}, keywords = {Bandwidth, Costs, Embedded systems, HTML, Information analysis, Integrated multiprotocol, ISDN card phone, Laptop computers, Mobile phones, Personal computers, Personal digital assistants, Proxy servers, Voice/data communication systems, Web browsers}, url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-4344632311\&partnerID=40\&md5=9242e761d5eedb61880ca004cdaa873d}, author = {Maroulis, D. and Aronis, S. and Nassiapoulou, V. and Grammenos, N. and Costas Vassilakis} } @conference {gorilas2003, title = {E-forms services for the Public Sector: Shifting Development Effort from Programmers to Domain Experts}, booktitle = {Proceedings of e-Challenges 2003}, year = {2003}, month = {10}, abstract = {E-forms have a central role in a significant number of e-government services. This paper presents a knowledge-based technical platform aiming to assist public sector employees to generate online transaction services by simplifying their development, maintenance and integration with installed IT systems. At the heart of this platform lies the knowledge and transaction services repository. This repository consists of a number of XML document types that incorporate all necessary details for creating and managing online transaction services. The main underlying idea is to provide a platform with intuitive interfaces that can be used directly by domain experts thus minimising the need for personnel with IT skills. This platform is currently under development within the IST SmartGov project.}, author = {Stelios Gorilas and Costas Vassilakis and Tomas Pariente Lobo and E. Tambouris} } @article {Vassilakis2003315, title = {A framework for managing the lifecycle of transactional e-government services}, journal = {Telematics and Informatics}, volume = {20}, number = {4}, year = {2003}, note = {cited By (since 1996) 13}, pages = {315-329}, abstract = {Filling and submission of electronic forms is a key issue for e-government, since most electronic services offered in this context include some variant of electronic forms. Insofar, IT experts are placed in the centre of electronic forms services lifecycles, undertaking the analysis, design, implementation and maintenance phases. This practice, however, implies various impediments, such as the need for multitudinous teams with diverse skills. In this paper, we present experiences from developing and maintaining a set of electronic services for the Greek Ministry of Finance, and propose an approach to handling electronic services{\textquoteright} lifecycle that balances responsibilities between domain experts and IT professionals. This approach enables a more holistic management of the electronic service lifecycle, by employing modelling and representation in high levels of abstraction and incorporating tools for automatically generating operative service instances from these high-level descriptions. Β{\textcopyright} 2003 Elsevier Science Ltd. All rights reserved.}, keywords = {Communication, Electronic forms, Information science, Information technology}, doi = {10.1016/S0736-5853(03)00011-X}, url = {https://www.sciencedirect.com/science/article/abs/pii/S073658530300011X}, author = {Costas Vassilakis and Laskaridis, G. and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @conference {DBLP:conf/caise/VassilakisLRG03, title = {Improving e-Form Layout Through Analysis of Form Semantics and Validation Checks}, booktitle = {CAiSE Short Paper Proceedings}, year = {2003}, month = {6}, abstract = {Transaction services offered by public authorities vary from simple forms with few fields to multi-form compound documents with hundreds of input areas. In the latter case, field placement within forms is of particular importance for facilitating the filling and error correction processes. In this paper we present an approach to improving the form layout by exploiting validation checks that are usually associated with electronic forms, as well as semantic information that may be attached to form fields by designers.}, url = {http://ceur-ws.org/Vol-74/files/FORUM_38.pdf}, author = {Costas Vassilakis and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @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 {667640, title = {An Object-Oriented Approach for Designing Administrative E-forms and Transactional E-services}, booktitle = {OOIS {\textquoteright}02: Proceedings of the 8th International Conference on Object-Oriented. Information Systems}, year = {2002}, month = {9}, pages = {19{\textendash}30}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Although electronic transaction services are considered to be a necessity for e-government, it has not been possible insofar to unleash their full potential. E-forms are central to the development of e-government, being a basic means for implementing the majority of the public services considered as required for local and central public administration authorities. In this paper, we present an object-oriented model for e-form-based administrative services, which spans the e-service lifecycle, including development, deployment and use by enterprises and citizens, data collection and communication with legacy information systems. The proposed approach encompasses semantic, structural and active aspects of e-forms, providing thus an inclusive framework for modelling electronic services.}, isbn = {3-540-44087-9}, doi = {10.1007/3-540-46102-7_6}, author = {D. Gouscos and S. Rouvas and Costas Vassilakis and P. Georgiadis} } @conference {Georgiadis_2002, title = {SmartGov: A Knowledge-Based Platform for Transactional Electronic Services}, booktitle = {Lecture Notes in Computer Science}, year = {2002}, month = {9}, pages = {362-369}, publisher = {Springer Berlin Heidelberg}, organization = {Springer Berlin Heidelberg}, abstract = {Public transaction services (such as e-forms) although perceived the future of e-government have not yet realised their full potential. E-forms have a significant role in e-government, as they are the basis for implementing most of the twenty public services that all member states have to provide to their citizens and businesses. The aim of the SmartGov project is to specify, develop, deploy and evaluate a knowledge-based platform to assist public sector employees to generate online transaction services by simplifying their development, maintenance and integration with already installed IT systems. This platform will be evaluated in two European countries (in one Ministry and one Local Authority). This paper outlines key issues in the development of the SmartGov system platform.}, doi = {10.1007/978-3-540-46138-8_59}, url = {https://link.springer.com/chapter/10.1007/978-3-540-46138-8_59}, author = {P. Georgiadis and Giorgos Lepouras and Costas Vassilakis and G. Boukis and E. Tambouris and S. Gorilas and E. Davenport and A. Macintosh and J. Fraser and D. Lochhead} } @conference {650426, title = {Transactional e-Government Services: An Integrated Approach}, booktitle = {EGOV {\textquoteright}02: Proceedings of the First International Conference on Electronic Government}, year = {2002}, month = {9}, pages = {276{\textendash}279}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Although form-based transactional services are fundamental to electronic government activities, their widespread does neither meet the citizen{\textquoteright}s expectations, nor the potential offered by state-of-the-art technologies. Besides any bureaucratic impediments, the primary reason for this is that traditional software engineering approaches cannot satisfactorily handle all the aspects of electronic services lifecycle. In this paper we present experiences from developing and maintaining a set of electronic services for the Greek Ministry of Finance, and propose a new approach for handling electronic service projects. The proposed approach has been successfully employed for developing extensions to the existing services, as well as some new ones.}, isbn = {3-540-44121-2}, doi = {10.1007/978-3-540-46138-8_44}, url = {http://link.springer.com/chapter/10.1007\%2F978-3-540-46138-8_44}, author = {Costas Vassilakis and Laskaridis, G. and Giorgos Lepouras and S. Rouvas and P. Georgiadis} } @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} } @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.} } @article {Vassilakis1998335, title = {Implementation of transaction and concurrency control support in a temporal DBMS}, journal = {Information Systems}, volume = {23}, number = {5}, year = {1998}, note = {cited By (since 1996) 2}, pages = {335{\textendash}350}, abstract = {Transactions and concurrency control are significant features in database systems, facilitating functions both at user and system level. However, the support of these features in a temporal DBMS has not yet received adequate research attention. In this paper, we describe the techniques developed in order to support transaction and concurrency control in a temporal DBMS that was implemented as an additional layer to a commercial DBMS. The proposed techniques make direct use of the transaction mechanisms of the DBMS. In addition, they overcome a number of limitations such as automatic commit points, lock release and log size increment, which are imposed by the underlying DBMS. Our measurements have shown that the overhead introduced by these techniques is negligible, less than 1\% in all cases. The approach undertaken is of general interest, it can also be applied to non-temporal DBMS extensions. Copyright Β{\textcopyright} 1998 Elsevier Science Ltd. All rights reserved.}, keywords = {Concurrency control, Data structures, Database systems, Temporal databases}, doi = {10.1016/S0306-4379(98)00015-5}, url = {https://doi.org/10.1016/S0306-4379(98)00015-5}, author = {Costas Vassilakis and N. Lorentzos and P. Georgiadis} } @conference {754888, title = {Implementing Embedded Valid Time Query Languages}, booktitle = {DEXA {\textquoteright}98: Proceedings of the 9th International Conference on Database and Expert Systems Applications}, year = {1998}, month = {8}, pages = {561{\textendash}572}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Application development on top of database systems is heavily based on the existence of embedded and 4GL languages. However, the issue of designing and implementing embedded or 4GL temporal languages has not been addressed insofar. In this paper, we present a design approach for implementing an embedded temporal language that supports valid time. Furthermore, we introduce implementation techniques that can be used for implementing any embedded temporal language that supports valid time on top of a DBMS.}, isbn = {3-540-64950-6}, doi = {10.1007/BFb0054514}, author = {Costas Vassilakis and P. Georgiadis and Sellis, Timos K.} } @conference {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} } @conference {719700, title = {Transaction Support in a Temporal DBMS}, booktitle = {Proceedings of the International Workshop on Temporal Databases}, year = {1995}, month = {9}, pages = {255{\textendash}271}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {London, UK}, abstract = {Transactions are a significant concept in database systems, facilitating functions both at user and system level. However transaction support in temporal DBMSs has not yet received enough research attention. In this paper, we present techniques for incorporating transaction support in a temporal DBMS, which is implemented as an additional layer to a commercial RDBMS. These techniques overcome certain limitations imposed by the underlying RDBMS, and avoid excessive increment of the log size.}, isbn = {3-540-19945-4}, doi = {10.1007/978-1-4471-3033-8_14}, url = {http://link.springer.com/chapter/10.1007\%2F978-1-4471-3033-8_14}, author = {Costas Vassilakis and N. Lorentzos and P. Georgiadis} } @conference {1993-kassapidis-hci, title = {Comparative Study of Protocols of the Transport Layer for Multimedia Applications}, booktitle = {Proceedings of the 4th Hellenic Conference on Informatics}, year = {1993}, month = {12}, pages = {105-118}, abstract = {The forthcoming use of multimedia applications will require powerful computers and high performance networks. While great progress has been made to the physical layer of networks, the upper software layers of the OSI reference model have not kept up pace with them. This paper presents the demands imposed by multimedia applications on the underlying networks and their mapping to transport layer services, that protocols implementing it must provide. Four well-known transport layer protocols are briefly presented (TCP, TP4, VMTP, HSTP/XTP). The mechanisms employed by each one of those are studied and their suitability for demanding multimedia environments are evaluated. We conclude that much more effort needs to be made on the transport layer protocols so that high performance network architectures will be available to fullfill the diverse requirements of tomorrow{\textquoteright}s multimedia applications.}, url = {http://cst.uop.gr/images/papers/1993-kassapidis-hci.pdf}, author = {Kassapidis, P. and Costas Vassilakis and M. Nikolaidou and P. Georgiadis and Votsis, Gr. and Pronios, N.} } @conference {1993-boukouvalas-hci, title = {An Enhanced System for File Access in a Distributed UNIX Environment}, booktitle = {Proceedings of the 4th Hellenic Conference on Informatics}, year = {1993}, month = {12}, abstract = {In this study we present an Enhanced File System for a Distributed Unix Environment. The Enhanced Unix File System implements a flexible protection mechanism for files and directories. It is based on the concept of Access Control Lists (ACL), which allows different permissions for files and directories to be given to specific users. His work was developed under the SunOS/NFS distributed environment, using Remote Procedure Calls (RPC) to implement the communication between the client and the server. The system consists of a daemon process working as a server and a set of client processes that provide different file and directory services. There may be running many different servers and clients over the same network. The client processes transparently locate the appropriate server for each transaction. The system also provides an open programming environment for the development of new applications. Both the user and the programmer interface of the system are kept close to standard UNIX.}, url = {http://cst.uop.gr/images/papers/1993-kassapidis-hci.pdf}, author = {Boucouvalas, C. and Costas Vassilakis and P. Georgiadis} } @conference {1993-vassilakis-hci, title = {A Methodology for the Implementation of Software for the Design of Distributed Systems}, booktitle = {Proceedings of the 4th Hellenic Conference on Informatics}, year = {1993}, month = {12}, pages = {673{\textendash}686}, abstract = {As the use of distributed systems is spreading, and applications designed for such systems become more and more demanding, optimal design of distributed systems becomes a critical issue. Designing a distributed system has become more complex, due to the number of alternatives for each decision that must be made and because of the existence of many parameters which influence the overal performance of the distributed system. Thus, it is necessary to use software tools, capable of accepting a description of the user{\textquoteright}s requirements and suggesting solutions to the problem of designing a distributed system which meets the user{\textquoteright}s requirements. In this paper, we present a disciplined approach to the construction of such a software tool, which combines methods from the Artificial Intelligence domain, that are used in order to design the distributed system, along with simulation techniques, used to estimate the system{\textquoteright}s overall performance.}, author = {Costas Vassilakis and P. Georgiadis and D. Lelis and D. Mouzakis and M. Nikolaidou} } @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} }