Costas Vassilakis | University of the Peloponnese (original) (raw)

Papers by Costas Vassilakis

Collaborative filtering formulates personalized recommendations by considering ratings submitted ... more Collaborative filtering formulates personalized recommendations by considering ratings submitted by users. Collaborative filtering algorithms initially find people having similar likings, by inspecting the similarity of ratings already present in the ratings database. Users exhibiting high similarity regarding their likings are classified as "near neighbors" (NNs) and the ratings entered by each user's near neighbors drive the formulation of recommendations for that user. To quantify the similarity between users, in order to determine a user's NNs, a similarity metric is used. Insofar, similarity metrics proposed in the literature either consider all user ratings equally or take into account temporal variations within the users' or items' ratings history. However users' ratings are co-shaped according to the experiences that they had in the past; therefore if two users enter similar (or dissimilar) ratings for an item while having experienced-to a large extent-the same items in the past, this constitutes stronger evidence about user similarity (or dissimilarity). Insofar however, no similarity metric takes into account this aspect. In this work, we propose and evaluate an algorithm that considers the common item rating past when computing rating predictions, in order to increase rating prediction accuracy.

Algorithms

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

The GPA is a universally recognised and utilised metric of academic performance that is considere... more The GPA is a universally recognised and utilised metric of academic performance that is considered to also measure a student’s potential for academic performance in the future. In this short communication we examine to what extent the GPA of the first grade of high school predicts performance in the later grades of high school, either generally (as classified in excellent student, strong student, weak student or very weak student) or more accurately (as indicated by the exact GPA in the next grade). We also put to the test the widely held notion that it might be best if core courses such as language and mathematics contributed more to the calculation of the GPA compared to secondary courses such as physical education or music. Our findings confirm the predictive properties of the GPA but strongly rebut the notion that a weighted GPA might achieve a better reflection of students’ potential. The study is based on the academic records of every student in Greece that progressed from fir...

Big Data and Cognitive Computing

Collaborative filtering has proved to be one of the most popular and successful rating prediction... more Collaborative filtering has proved to be one of the most popular and successful rating prediction techniques over the last few years. In collaborative filtering, each rating prediction, concerning a product or a service, is based on the rating values that users that are considered “close” to the user for whom the prediction is being generated have given to the same product or service. In general, “close” users for some user u correspond to users that have rated items similarly to u and these users are termed as “near neighbors”. As a result, the more reliable these near neighbors are, the more successful predictions the collaborative filtering system will compute and ultimately, the more successful recommendations the recommender system will generate. However, when the dataset’s density is relatively low, it is hard to find reliable near neighbors and hence many predictions fail, resulting in low recommender system reliability. In this work, we present a method that enhances rating ...

Lecture Notes in Computer Science, 2022

Information

One of the typical goals of collaborative filtering algorithms is to produce rating predictions w... more One of the typical goals of collaborative filtering algorithms is to produce rating predictions with values very close to what real users would give to an item. Afterward, the items having the largest rating prediction values will be recommended to the users by the recommender system. Collaborative filtering algorithms can be applied to both sparse and dense datasets, and each of these dataset categories involves different kinds of risks. As far as the dense collaborative filtering datasets are concerned, where the rating prediction coverage is, most of the time, very high, we usually face large rating prediction times, issues concerning the selection of a user’s near neighbours, etc. Although collaborative filtering algorithms usually achieve better results when applied to dense datasets, there is still room for improvement, since in many cases, the rating prediction error is relatively high, which leads to unsuccessful recommendations and hence to recommender system unreliability....

Future Internet

Exploitation and use of disruptive technologies, such as the Internet of Things, recommender syst... more Exploitation and use of disruptive technologies, such as the Internet of Things, recommender systems, and artificial intelligence, with an ambidextrous balance, are a challenge, nowadays. Users of the technologies, and stakeholders, could be part of a new organisational model that affects business procedures and processes. Additionally, the use of inclusive participatory organisational models is essential for the effective adoption of these technologies. Such models aim to transform organisational structures, as well. Public organisations, such as the parliament, could utilise information systems’ personalisation techniques. As there are a lot of efforts to define the framework, the methodology, the techniques, the platforms, and the suitable models for digital technologies adoption in public organisations, this paper aims to provide a literature review for disruptive technology inclusive use in parliaments. The review emphasises the assessment of the applicability of the technologi...

2020 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM)

Terrorism is a major disincentive to tourism. It affects both a country or area's tourists as wel... more Terrorism is a major disincentive to tourism. It affects both a country or area's tourists as well as local residents and staff. On the one hand, the prospective tourist is likely to avoid traveling to a high-risk country due to safety concerns, and thus lose the opportunity to visit it, while, on the other hand, the tourism of the country would decline. This work solves the above-mentioned problem by (1) showing that reasonably safe visits to highrisk countries can be predicted with high precision, using limited information, including data on attacks and fatalities from recent years, which is widely available, and (2) creating an algorithm that recommends these periods to potential travellers. The findings of this work would be useful for tourists, citizens, businesses and operators, as well as related stakeholders.

Information

The typical goal of a collaborative filtering algorithm is the minimisation of the deviation betw... more The typical goal of a collaborative filtering algorithm is the minimisation of the deviation between rating predictions and factual user ratings so that the recommender system offers suggestions for appropriate items, achieving a higher prediction value. The datasets on which collaborative filtering algorithms are applied vary in terms of sparsity, i.e., regarding the percentage of empty cells in the user–item rating matrices. Sparsity is an important factor affecting rating prediction accuracy, since research has proven that collaborative filtering over sparse datasets exhibits a lower accuracy. The present work aims to explore, in a broader context, the factors related to rating prediction accuracy in sparse collaborative filtering datasets, indicating that recommending the items that simply achieve higher prediction values than others, without considering other factors, in some cases, can reduce recommendation accuracy and negatively affect the recommender system’s success. An ex...

2020 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM), 2020

Every day, many people use at least one social network (or social media) account. This developmen... more Every day, many people use at least one social network (or social media) account. This development has been boosted by the rapid growth of technology, making both smartphones and mobile data much more accessible and inexpensive. Therefore, the number of social networks users is growing rapidly, accounting more than 1 billion active users worldwide. The ease of use, as well as the ability to communicate without spatial and temporal restrictions underpinned the rapid increase of the popularity of social networks, as well as their wide acceptance by the general public. This popularity influences people's opinion on many issues, shapes consumer habits and behaviour, mood, etc. The work of many scientists across multiple disciplines has focused on studying social media from various perspectives, including marketing, journalism and sociology. This paper investigates how trending information from social media can be used to match topics of interest from cultural database indices. Matches identified in this process are then presented to cultural venue curators, who can then review matches, mark them as useful or reject them, and exploit them for various tasks, and most notably for the promotion of the venue and its content. More specifically, we have developed an application, which collects the 10 most popular twitter trends and then matches their content with the contents of a given cultural database. Using the results of this match, items from the database that may be related to current issues may be recommended to the user. As a result, these matches, after being inspected and approved by the administrator, can be used to attract the interest of the target audience, highlighting the correlation of current issues with the database's items.

Proceedings of the 11th International Conference on Management of Digital EcoSystems, 2019

This work presents a platform for linked legislative data to engage citizens in transparent and e... more This work presents a platform for linked legislative data to engage citizens in transparent and effective democracies. With a focus on scaling up participatory approaches from local to national level, the approach extends well established and open source tools and technologies, to build mobile monitoring and analysis tools that increase transparency of law-making and implementation to citizens. This is achieved by combining open data and open services with user and citizen generated content, in order to address citizen's needs in the context of open government. Data and feeds from trusted sources are interconnected with new and re-purposed data feeds generated by users via the social web to form a meaningful, searchable, customizable, re-usable and open data-focused personalised mobile public service approach. The framework exploits the social aspects of open data, as well as the training of users, citizens and public servants to be able to understand and demand useful public open data, as well as facilitate the opening of more data. CCS CONCEPTS • Information systems → Extraction, transformation and loading • Information systems → Entity resolution • Human-centered computing → User studies • Human-centered computing → Empirical studies in HCI • Social and professional topics → Government technology policy

Proceedings of the 2019 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining, 2019

Online advertising benefits by recommender systems since the latter analyse reviews and rating of... more Online advertising benefits by recommender systems since the latter analyse reviews and rating of products, providing useful insight of the buyer perception of products and services. When traditional recommender system information is enriched with social network information, more successful recommendations are produced, since more users' aspects are taken into consideration. However, social network information may be unavailable since some users may not have social network accounts or may not consent to their use for recommendations, while rating data may be unavailable due to the cold start phenomenon. In this paper, we propose an algorithm that combines limited collaborative filtering information, comprised only of users' ratings on items, with limited social network information, comprised only of users' social relations, in order to improve (1) prediction accuracy and (2) prediction coverage in collaborative filtering recommender systems, at the same time. The proposed algorithm considerably improves rating prediction accuracy and coverage, while it can be easily integrated in recommender systems.

European Journal of Engineering and Technology Research, 2020

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

Antoniou, A., Vassilakis, C., Wallace, M., Lepouras, G., Poulopoulos, V. (2017). Experiences from... more Antoniou, A., Vassilakis, C., Wallace, M., Lepouras, G., Poulopoulos, V. (2017). Experiences from the development of thematic routes in 3 Greek museums (in Greek). Proceedings of the Europmed 2017, 2<sup>nd</sup> Panhellenic Conference on Digitization of Cultural Heritage.

Heritage, 2018

Social media usage is affecting peoples’ views through opinion sharing, a fact that has started t... more Social media usage is affecting peoples’ views through opinion sharing, a fact that has started to attract cultural institutions, as it is possible that this procedure can possibly be a part of a museum experience. As the main goal of a cultural institution is the maximization of senses stimulation, the device that is offered to the visitors’ hands everyday and every moment, becomes an important tool for the art spaces. In this notion we perform research on issues that can be of great importance for the museum’s online presence and attraction. We focus on establishing the personality of influencers related to culture, as well as the characteristics of qualitative discussions on the social media. Crosscult Project is an EU funded project, that aims to spur a change in the way European citizens appraise History, and sets that basis of our research as the experiments are conducted within its scope of. Through the experimental procedure, we collect information in order to define the cha...

2019 10th International Conference on Information, Intelligence, Systems and Applications (IISA), 2019

Natural Language Generators may generate texts that are linguistically enriched. These may result... more Natural Language Generators may generate texts that are linguistically enriched. These may result in significantly improved synthetic speech. At the same time, the generators produce pieces of plain text that may span between a single word to a full sentence. Additionally, traditional natural language generators have limited domain coverage, resulting in restricted language analysis of the generated texts. For those cases the enriched input to the speech synthesizer, required for high quality speech synthesis, can be provided by analysing the plain text. This work reports on the method for automatic domain dependent annotation of plain text, through the utilisation of the linguistic information from rich generated text. The synthetic speech from the resulting prosody models is evaluated by human participants showing annotation results for plain text quite on par with the rich generated text. This leads to improved perceived naturalness of the synthesized speech.

Proceedings of the 11th International Conference on Management of Digital EcoSystems, 2019

In the modern information society, learning is no longer just about obtaining factual knowledge, ... more In the modern information society, learning is no longer just about obtaining factual knowledge, but more about general skills on how and where to apply available knowledge and obtain new knowledge in order to solve new problems. Such skills include abilities to connect and organize ideas, fill gaps in knowledge structures, evaluate evidence, argue with new information, test and modify, predict, clarify, generate questions, learn new concepts, make unexpected connections, reflect, analyze, synthesize and loop back. This work presents the Immersion framework, a digital ecosystem for adaptive smart learning environments for interactive mixed reality driven methods to foster learners' self-regulating skill development.

HCI-VR lab in Short. The Human-Computer Interaction and Virtual Reality Lab, at the Department of... more HCI-VR lab in Short. The Human-Computer Interaction and Virtual Reality Lab, at the Department of Informatics and Telecommunications of the University of Peloponnese, aims to conduct high quality research in areas related to the analysis, design, development, and evaluation of HCI and VR systems and applications, and in parallel to support the teaching requirements of the department in the respective field. Over the last years the HCI-VR lab particularly focuses on Cultural Heritage and develops technologies primarily for spaces of cultural heritage that cover the diverse needs of heterogeneous audiences providing holistic visitor experience. The HCI-VR lab is actively participating in National and European projects on Cultural Heritage, such as FP7 Experimedia (https://hci-vr.dit.uop.gr/experimedia), H2020 CrossCult (www.crosscult.eu) and multiple projects from the National Strategic Reference Framework.

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

Algorithms

Big Data and Cognitive Computing

Lecture Notes in Computer Science, 2022

Information

Future Internet

2020 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM)

Information

2020 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM), 2020

Proceedings of the 11th International Conference on Management of Digital EcoSystems, 2019

Proceedings of the 2019 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining, 2019

European Journal of Engineering and Technology Research, 2020

Heritage, 2018

2019 10th International Conference on Information, Intelligence, Systems and Applications (IISA), 2019

Proceedings of the 11th International Conference on Management of Digital EcoSystems, 2019

Η πρόοδος των κινητών τεχνολογιών έχει δημιουργήσει ευκαιρίες για πιο αποτελεσματική διάχυση πλη... more Η πρόοδος των κινητών τεχνολογιών έχει δημιουργήσει ευκαιρίες για πιο αποτελεσματική διάχυση πληροφοριών πολιτιστικής κληρονομιάς σε όλες τις ενδιαφερόμενες πλευρές και ιδιαίτερα στους τουρίστες που βρίσκονται εν κινήσει. Πολλοί άνθρωποι σήμερα είναι εξοπλισμένοι με έξυπνα κινητά ή ταμπλέτες, τα οποία διαθέτουν διατάξεις εντοπισμού θέσης, όπως π.χ. GPS και πυξίδες, ενώ παράλληλα διαθέτουν και πρόσβαση στο διαδίκτυο. Αυτές οι κινητές συσκευές μπορούν να χρησιμοποιηθούν αποτελεσματικά για επίκαιρη και προσαρμοσμένη στις προσωπικές προτιμήσεις των χρηστών παροχή πληροφοριών πολιτιστικής κληρονομιάς. Επιπρόσθετα, οι υπολογιστικοί πόροι των κινητών αυτών συσκευών είναι πλέον επαρκείς για να υποστηρίξουν τη χρήση τεχνικών επαυξημένης πραγματικότητας, οι οποίες παρέχουν μία «ζωντανή» και ενδιαφέρουσα εμπειρία στους χρήστες. Ωστόσο, το ίδιο περιεχόμενη πρέπει επίσης να διαχυθεί σε χρήστες σταθερών υπολογιστών. Στην παρούσα εργασία, παρουσιάζουμε τον σχεδιασμό και την ανάπτυξη μιας πλατφόρμας για παρουσίαση και διάχυση πληροφοριών πολιτιστικής κληρονομιάς που παρέχει υποστήριξη για κινητές συσκευές, η οποία είναι εμπλουτισμένη με δυνατότητες επαυξημένης πραγματικότητας και ολοκλήρωσης με κοινωνικά δίκτυα.

This paper describes a technique for interceding between users and the information that they bro... more This paper describes a technique for interceding between users and the information that they browse. This facility, that we term 'dynamic annotation', affords a means of editing Web page content 'on-the-fly' between the source Web server and the requesting client. Thereby, we have a generic way of modifying the content displayed to local users by addition, removal or reorganising any information sourced from the World-Wide Web, whether this derives from local or remote pages. For some time, we have been exploring the scope for this device and we believe that it affords many potential worthwhile applications. Here, we describe two varieties of use. The first variety focuses on support for individual users in two contexts (second-language support and second language learning). The second variety of use focuses on support for groups of users. These differing applications have a common goal which is content enrichment of the materials placed before the user. Dynamic annotation provides a potent and flexible means to this end.

Manual ontology development is clearly a strenuous task. Whilst a variety of ontological enginee... more Manual ontology development is clearly a strenuous task. Whilst a variety of ontological engineering methodologies exist, their actual application is far from trivial, mainly due to the widely diverse nature of the tasks involved. In this work we study these tasks and identify the different types of human experts that are best suited to perform each one. As a result, we present a cooperative version of an ontological engineering methodology, together with a graphical tool that supports it.

A requirement for electronic government initiatives to succeed is the ability to offer a citizen... more 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'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.

Transactions are a significant concept in database systems, facilitating functions both at user ... more 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.

Web services are functional, independent components that can be called over the web to perform a... more Web services are functional, independent components that can be called over the web to perform a task. Besides being used individually to deliver some well-specified functionality, web services may be used as building blocks that can be combined to implement a more complex function. In such compositions, typically some web services produce results that are used as input for web services that will be subsequently invoked. In the execution schemes currently employed, web services producing intermediate results deliver them to some "coordinating entity", which arranges the forwarding of these intermediate results to web services that require them as input. In this paper we present an execution scheme that employs direct communication between producers and consumers of intermediate results. Besides performance improvement stemming from reduction of network communication, this scheme permits consumer web services to employ simpler authenticity and integrity verification algorithms on incoming parameters. when the producer web service is considered trustworthy. Β©2006 IEEE.

The paper addresses issues related to client/server technologies and specifically the effectiven... more The paper addresses issues related to client/server technologies and specifically the effectiveness of server-side programming techniques. The motive for this study was the need to create a lightweight and dynamic navigational aid for use in a web site. Towards this goal a number of possible solutions were considered and for two of them an experiment was run to determine the best suited for our case. The rest of the paper outlines our findings.

Web sites employ dynamically generated pages for content delivery more and more often, in order ... more Web sites employ dynamically generated pages for content delivery more and more often, in order to increase their flexibility and provide up-to-date information. This practice, however, increases server load dramatically, since each request results to the execution of code, which may involve processing and/or access to information repositories. In this paper we present a scheme for maintaining a server-side cache of dynamically generated pages, allowing for cache consistency maintenance, without placing heavy burdens on application programmers. We also present insights to architecture scalability and some results obtained from conducted experiments.

Electronic government employs electronic services to facilitate interaction with citizens and en... more Electronic government employs electronic services to facilitate interaction with citizens and enterprises and deliver a rich and high quality spectrum of services. Development of electronic services can be greatly assisted, both in terms of development cost and roll-out time, by exploiting the reusability inherent in them. Reusability may be promoted by identifying reusable objects in the context of electronic service development, building and populating a repository with such components and providing the means for developers to locate, extract and adapt them to suit the task at hand. In this paper we analyse electronic services to recognise reusable components and present means and techniques that empower electronic service developers to build electronic services through reusable components.

Although form-based transactional services are fundamental to electronic government activities, ... more Although form-based transactional services are fundamental to electronic government activities, their widespread does neither meet the citizen'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.

In the context of service-oriented computing, the introduction of the Quality-of-Service (QoS) a... more In the context of service-oriented computing, the introduction of the Quality-of-Service (QoS) aspect leads to the need to adapt the execution of programs to the QoS requirements of the particular execution. This is typically achieved by finding alternate services that are functionally equivalent to the ones originally specified in the program and whose QoS characteristics closely match the requirements, and invoking the alternate services instead of the originally specified ones; the same approach can also be employed for tackling exceptions. The techniques proposed insofar, however, cannot be applied in a secure context, where data are encrypted and signed for the originally intended recipient. In this paper, we introduce a framework for facilitating adaptation in the context of secure SOA.

Econsultations constitute an effective means to inclusive and informed participation of citizens... more 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.

Application development on top of database systems is heavily based on the existence of embedded... more 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.

As the use of distributed systems is spreading, and applications designed for such systems becom... more 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's requirements and suggesting solutions to the problem of designing a distributed system which meets the user'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's overall performance.

Human History, is a huge mesh of interrelated facts and concepts, spanning beyond borders, encom... more Human History, is a huge mesh of interrelated facts and concepts, spanning beyond borders, encompassing global aspects and finally constituting a shared, global experience. This is especially the case regarding European history, which is highly interconnected by nature; however, most History-related experiences that are today offered to the greater public, from schools to museums, are siloed. The CrossCult project aims to provide the means for o ering citizens and cultural venue visitors a more holistic view of history, in the light of cross-border interconnections among pieces of cultural heritage, other citizens viewpoints and physical venues. To this end, the CrossCult project will built a comprehensive knowledge base encompassing information and semantic relationships across cultural information elements, and will provide the technological means for delivering the contents of this knowledge base to citizens and venue visitors in a highly personalized manner, creating narratives for the interactive experiences that maximise situational curiosity and serendipitous learning. The CrossCult platform will also exploit the cognitive/emotional profiles of the participants as well as temporal, spatial and miscellaneous features of context, including holidays and anniversaries, social media trending topics and so forth.

In this paper a novel two-priority network schema is presented, and exemplified through its appl... more 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© 2007 IEEE.

In this paper the modeling of Omega Networks supporting multi-class routing traffic is presented... more 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© 2008 IEEE.

Multilayer MINs have emerged mainly due to the increased need for routing capacity in the presen... more 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© 2009 IEEE.

Banyan Networks are a major class of Multistage Interconnection Networks (MINs). They have been ... more Banyan Networks are a major class of Multistage Interconnection Networks (MINs). They have been widely used as efficient interconnection structures for parallel computer systems, as well as switching nodes for high-speed communication networks. The performance of them is mainly determined by their communication throughput and their mean packet delay. In this paper we use a model that is based on a universal performance factor, which includes the importance aspect of each of the above main performance factors (throughput and delay) in the design process of a MIN. The model can also uniformly be applied to several representative networks. The complexity of the model requires to be investigated by time-consuming simulations. In this paper we study a typical (8X8) Baseline Banyan Switch that consists of (2X2) Switching Elements (SEs). The objective of this simulation is to determine the optimal buffer size for the MIN stages under different conditions.

Multistage Interconnection Networks (MINs) are frequently used for connecting processors in para... more Multistage Interconnection Networks (MINs) are frequently used for connecting processors in parallel computing systems or constructing high speed networks such as ATM (based on Asynchronous Transfer Mode) and Gigabit Ethernet Switches. New applications require distributed computing implementations, but old networks are too slow to allow efficient use of remote resources. Moreover, multimedia are considered as applications with high bandwidth requirements. Some of them are also sensitive to packet loss and claim reliable data transmission. Specific applications require bulk data transfers for database replication or load balancing and therefore packet loss minimization is necessary in order to increase the performance of them. The demand for high performance multimedia services such as full motion video on demand is becoming an increasingly important driving force in the communication market in the Digital Age. Thus, the performance of MINs is a crucial factor, which we have to take into account in the design of new applications. Their performance is mainly determined by their communication throughput and cell latency, which have to be investigated either by time-consuming simulations or approximated by mathematical models. In this paper we investigate the performance of MINs in order to determine optimal values for hardware parameters under diferent operating conditions.

Transactions and concurrency control are significant features in database systems, facilitating ... more 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© 1998 Elsevier Science Ltd. All rights reserved.

Electronic commerce, nowadays, is trying to extend its target audience and elevate the quality o... more Electronic commerce, nowadays, is trying to extend its target audience and elevate the quality of services offered to end-users. Two important directions towards meeting these goals are the embracement of mobile users, whose number grows following the advent of communication technologies, and the inclusion of context-aware features in the delivered services to improve the efficiency of the dialogues between users and systems. The context taken into account may involve characteristics regarding the human user, the geographical location and the time of access, the devices employed to access the service, the network through which the user communicates with the system, the nature of the transaction carried out and so forth. It is clear that the development and successful operation of mobile and context-aware e-commerce introduce new challenges. In order to tackle such challenges, new methodologies, tools, architectures and platforms should be made available to assist analysts, designers, developers and operators in handling the various phases of the Mobile and Context-Aware E-Commerce Services (MCACS) lifecycle.

Documents submitted by citizens through electronic services deployed in the context of e-Governm... more 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.

On their route to the electronic era, organisations release on the web more and more complex for... more 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© 2005 Inderscience Enterprises Ltd.

Since the beginning of the electronic era, public administrations and enterprises have been deve... more Since the beginning of the electronic era, public administrations and enterprises have been developing services, through which citizens, businesses and customers can conduct their transactions with the offering entity. Each electronic service contains a substantial amount of knowledge in the form help texts, rules of use or legislation excerpts, examples, validation checks, etc. This knowledge has been extracted from domain experts when the services were developed, especially in the phases of analysis and design, and was subsequently translated into software. In the latter format though, knowledge cannot be readily used in organizational processes, such as knowledge sharing and development of new services. In this paper, we present an approach for reverse engineering electronic services in order to create knowledge items of high levels of abstraction, which can be used in knowledge sharing environments as well as in service development platforms. The proposed approach has been implemented and configured to generate artifacts for the SmartGov service development platform. Finally, an evaluation of the proposed approach is presented to assess its efficiency regarding various aspects of the reverse engineering process. Β© 2008 Elsevier B.V. All rights reserved.

With the need for electronic services to be developed and deployed more and more rapidly, it is ... more With the need for electronic services to be developed and deployed more and more rapidly, it is imperative that concrete models of electronic services are developed, to facilitate systematic work of electronic service stakeholders, concrete semantics and coherent representations across services developed within an organisation. Using the XML language to develop such a model, offers a number of additional advantages, such as rich semantics, facilitation of data interchange, extensibility, high abstraction levels and possibility for mechanical processing. In this paper we present the design aspects of an XML model for electronic services, which has been used for building a repository of interlinked elements representing e-services. A web-based interface for the management of this repository and a tool for automatically compiling e-service descriptions into executable images have been developed alongside. The model has been evaluated by a mixture of electronic service stakeholders, and the results of this evaluation are also presented.

Having realised the benefits resulting from delivering on-line public services in the context of... more Having realised the benefits resulting from delivering on-line public services in the context of electronic government, administrations strive to extend the spectrum of services offered to citizens and enterprises, as well as to engage multiple communication channels in service delivery, in order to increase the target audience and, consequently, the service effectiveness. Insofar, however, only the web channel has been sufficiently used for service delivery, whereas other channels have not been adequately exploited. One of the main reasons of this lag is the cost incurred for the development and maintenance of multiple versions of an electronic service, each version targeted to a different platform. In this paper, we present an approach and the associated tools for developing and maintaining electronic services that allows the automated production of different versions of the electronic service, each targeted to a specific platform. Β© 2006 Elsevier B.V. All rights reserved.

E-government initiatives have been proven to deliver significant benefits, both for suppliers of... more E-government initiatives have been proven to deliver significant benefits, both for suppliers of electronic services (public authorities and organizations) and for the public, to whom services are addressed. However, the pace with which electronic services are made available and adopted is lower than planned or expected; governments tend to be slow in releasing new services, and citizens often prefer to conduct business with the government through paper forms and physical presence, rather than using online methods. This indicates that certain barriers exist that hinder the transition to electronic services. In this paper, we present the results of a survey among electronic service stakeholder groups, to identify the most important barriers to electronic service development. Documentation of barriers is considered important, since administrations may take certain measures to overcome them. Hints on how specific barriers may be overcome are also provided.

In the context of electronic government, e-services are a valuable instrument for offering high ... more In the context of electronic government, e-services are a valuable instrument for offering high quality services to enterprises and individual citizens alike. While developing an e-service, it is usually possible to reuse elements that have already crafted for other e-services, such as personal detail forms or widgets for collecting social security numbers, decreasing thus both development effort and the time for deployment. A more generic framework for supporting reusability in development of e-services includes the identification of reusable objects, the creation and population of a repository containing such components, and the empowerment of developers with tools allowing for location, retrieval and adaptation of components for suiting their specific tasks. In this paper, we conduct an analysis to recognise e-service component that offer reusability opportunities and we present facilities and methods to enable e-service developers to exploit these opportunities while developing electronic services.

Filling and submission of electronic forms is a key issue for e-government, since most electroni... more 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' 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© 2003 Elsevier Science Ltd. All rights reserved.

The paper presents an integrated environment which enables museum personnel to catalogue and at ... more The paper presents an integrated environment which enables museum personnel to catalogue and at the same time publish online museum exhibits. The system is based on international standards and is highly customisable to cater the needs of a variety of museum types. Moreover, the underlying database allows storing for the same exhibit documentations for different audiences and in multiple languages, while it is extendable to accommodate new media types, languages, exhibits and information categories. The administrative part of the environment permits the restriction of certain functions to specific personnel roles, enforcing thus a general museum security policy regarding access to and modification of information. The environment presented is currently in use at the Athens University History Museum.

Queries in temporal databases often employ the coalesce operator, either to coalesce results of ... more Queries in temporal databases often employ the coalesce operator, either to coalesce results of projections, or data which are not coalesced upon storage. Therefore, the performance and the optimisation schemes utilised for this operator is of major importance for the performance of temporal DBMSs. Insofar, performance studies for various algorithms that implement this operator have been conducted, however, the joint optimisation of the coalesce operator with other algebraic operators that appear in the query execution plan has only received minimal attention. In this paper, we propose a scheme for combining the coalesce operator with selection operators which are applied to the valid time of the tuples produced from a coalescing operation. The proposed scheme aims at reducing the number of tuples that a coalescing operator must process, while at the same time allows the optimiser to exploit temporal indices on the valid time of the data.

In this paper, the modelling, analysis and performance evaluation of a novel architecture for in... more 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’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.

Next-generation network architectures strive to achieve high bandwidth and ultralow latency for ... more Next-generation network architectures strive to achieve high bandwidth and ultralow latency for the packets traversing the offered end-to-end paths. Multistage Interconnection Networks (MINs) are often employed for implementing NGNs, but while MINs are fairly flexible in handling varieties of traffic loads, they tend to quickly saturate under broadcast and multicast traffic, especially at increasing size networks. As a response to this issue, multilayer MINs have been proposed, however their performance prediction and evaluation has not been studied sufficiently insofar. In this paper, we evaluate and discuss the performance of multilayer MINs under multicast traffic, considering also two levels of packet priorities, since support for multiple QoS levels is an indispensible requirement for NGNs. Different offered loads and buffer size configurations are examined in this context, and performance results are given for the two most important network performance factors, namely packet throughput and delay. We also introduce and calculate a universal performance fac¬tor, which includes the importance aspect of each of the above main performance factors. The findings of this study can be used by NGN system designers in order to predict the performance of each configuration and adjust the design of their communication infrastructure to the traffic requirements at hand.

Contemporary networks support multiple priorities, aiming to differentiate the QoS levels offere... more Contemporary networks support multiple priorities, aiming to differentiate the QoS levels offered to individual traffic classes. Support for multiple priorities necessitates the introduction of a scheduling algorithm, to select each time the next packet to transmit over the data link. Class-based Weighted Fair Queuing (CBWFQ) scheduling and its variations, is widely used as a scheduling technique, since it is easy to implement and prevents the low-priority queues from starvation, i.e. receiving no service during periods of high-priority traffic. CBWFQ effectively thus offers low-priority queues the opportunity to transmit packets even though the high-priority queues are not empty. In this paper, we present the modeling and performance evaluation of a single-buffered, four-priority multistage interconnection network (MIN) operating under the CBWFQ scheduling policy. Performance evaluation is conducted through simulation, and the performance metrics obtained can be used by MIN designers to set the appropriate queue weights according to the expected traffic and the desired QoS levels for each priority class, delivering efficient thus systems.

In this paper, we model, analyze and evaluate the performance of a 2-class priority architecture... more In this paper, we model, analyze and evaluate the performance of a 2-class priority architecture for finite-buffered Multistage Interconnection Networks (MINs). The MIN operation modelling is based on a state diagram, which includes the possible MIN states, transitions and conditions under which each transition occurs. Equations expressing state and transition probabilities are subsequently given, providing a formal model for evaluating the MIN's performance. The proposed architecture's performance is subsequently analyzed using simulations; operational parameters, including buffer length, MIN size, offered load and ratios of high priority packets which are varied across experiments to gain insight on how each parameter affects the overall MIN performance. The 2-class priority MIN performance is compared against the performance of single priority MINs, detailing the performance gains and losses for packets of different priorities. Performance is assessed by means of the two most commonly used factors, namely packet throughput and packet delay, while a performance indicator combining both individual factors is introduced, computed and discussed. The findings of this study can be used by network and interconnection system designers in order to deliver efficient systems while minimizing the overall cost. The performance evaluation model can also be applied to other network types, providing the necessary data for network designers to select optimal values for network operation parameters.

Wireless Local Area Networks (WLANs) have developed into a viable technology to support multimed... more Wireless Local Area Networks (WLANs) have developed into a viable technology to support multimedia traffic and are expected to support multimedia services with guaranteed Quality of Service (QoS) for diverse traffic types (video, audio, and data). In this paper, we consider the incorporation of prediction into a generic distance-vector routing protocol for WLANs, evaluate the performance of the resulting routing scheme. Our study considers the enhancement of Distributed Bellman-Ford algorithm, which is a widely used algorithm, and assesses the effectiveness of the enhanced version on top of a fourth generation system (4-G). In order to compare the performance of the standard protocol against that of the prediction-enhanced version, we gather metrics for the two most important network performance factors, namely packet throughput and delay under different mobility and traffic conditions, using the simulation environment of NS-2. Both medium- and high-mobility configurations have been considered in this study.

Differentiated Services (DiffServ) and other scheduling strategies are now widespread in the tra... more Differentiated Services (DiffServ) and other scheduling strategies are now widespread in the traditional, “best effort” Internet. These Internet Architectures offer Quality of Service (QoS) guarantees for important customers at the same time as supporting less critical applications of lower priority. Strict priority queuing (PQ), weighted round robin (WRR), and class-based weighted fair queuing (CBWFQ) are three common scheduling disciplines for differentiation of services in telecommunication networks. In this paper, a comparative performance study of the above PQ, WRR and CBWFQ queuing scheduling policies applied on a double-buffered, 6-stage Multistage Interconnection Network (MIN) that natively supports a 2-class priority mechanism is presented and analyzed using simulation experiments. We also consider a 10-stage MIN, to validate that the conclusions drawn from the 6-stage MIN apply to MINs of different sizes. The findings of this paper can be used by MIN designers to optimally configure their networks.

Historic research involves finding, using, and correlating informationwithin primary and seconda... more Historic research involves finding, using, and correlating informationwithin primary and secondary sources, in order to communicate an understanding of past events. In this process, historians employ their scientific knowledge, experience, and intuition to formulate queries (who was involved in an event, when did an event occur etc.), and subsequently try to locate the pertinent information from their sources. In this article, the authors investigate how historians formulate queries, which query terms are chosen, and how historians proceed in searching for related information in sources. The insight gained from this investigation can be subsequently used for organizing documentswithin historical source repositories and building tools that will enable historians to access the needed informationmore rapidly and fully.

In this study we present a technique for the parallel optimisation of join queries that uses th... more In this study we present a technique for the parallel optimisation of join queries that uses the offered coarse-grain parallelism of the underlying architecture in order to reduce the CPU-bound optimisation overhead. The optimisation technique performs an almost exhaustive search of the solution space for small join queries and gradually, as the number of joins increases, it diverges towards iterative improvement. This technique has been developed on a low-parallelism transputer-based architecture, where its behaviour is studied for the optimisation of queries with many tens of joins.

In this work, the usage of ontologies for meeting requirements related to e-service composition,... more In this work, the usage of ontologies for meeting requirements related to e-service composition, e-service cataloguing, change management and administrative responsibility is examined. An ontology for e-government services is presented, covering various aspects of services, including administrative responsibility, meta-data, involved documents and legislation. Both the development and usage phase of the ontology are covered and directions for further exploitation of the potential offered by the ontological representation are given.

Transactional services are an indispensible part of e-government, since provision of services to... more Transactional services are an indispensible part of e-government, since provision of services to citizens and enterprises,as well as the interaction between the government and citizens-enterprises are modelled mainly through such services. Latest quantifications, however, show that the development of such services lags behind as compared both to the expectations of citizens-enterprises and to the efforts made by governments. This can be attributed, amongst other reasons, to the "traditional" approach to electronic service development, which treats each electronic service as an isolated software project. In this paper, we propose an e-service development platform, which covers the whole lifecycle of transactional services and facilitates the analysis, development, deployment and maintenance of these services.

We introduce a novel knowledge-based recommendation algorithm for leisure time information to be... more 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.

Firms and organizations are increasingly exploiting electronic channels to reach their customers... more Firms and organizations are increasingly exploiting electronic channels to reach their customers and create new business opportunities. To this end, electronic shops have been developed, either offering products from a single firm or encompassing multiple individual electronic stores, comprising thus electronic shopping malls. Two main concerns for e-commerce are personalization and enhancement of user experience. Personalization addresses the ability to offer content tailored to the preferences of each user or user group. Preferences may be explicitly declared by the user, or derived by the system through inspecting user interaction; if the system dynamically reacts to changes of visitor behavior, it is termed as adaptive. Enhancement of user experience is another major issue in e-commerce, given that 2D-images and texts on the screen are not sufficient to provide information on products aspects such as physical dimensions, textures and manipulation feedback. Multimedia presentations can also be used as a means for .information acceleration. for promoting "really new" products. This article aims to specify a system that exploits capabilities offered by adaptation and VR technologies to offer e-shoppers personalized and enhanced experiences, while addressing challenges related to the cost, complexity and effort of building and maintaining such a system.

This chapter presents an architecture for supporting the creation of adaptive virtual reality mu... more This chapter presents an architecture for supporting the creation of adaptive virtual reality museums on the web. It argues whether the task of developing adaptive virtual reality museums is a complex one, presenting key challenges, and should thus be facilitated by means of a supporting architecture and relevant tools. The proposed architecture is flexible enough to cater for a variety of user needs, and modular promoting extensibility, maintainability and tailorability. Adoption of this architecture will greatly simplify the development of adaptive virtual reality museums, reducing the needed effort to exhibit digitisation and user profile specification; user profiles are further refined dynamically through the user data recorder and the user modelling engine, which provide input for the virtual environment generator.

Reusability is the degree to which a software component or other work can be used in more than o... more Reusability is the degree to which a software component or other work can be used in more than one programs or software systems. e-Government is a prosperous area for the application of reusability, since the services offered to citizens from the same administration, or even different administrations, have common portions that can be developed only once and reused wherever appropriate. In this paper we present the design and implementation of an electronic service development environment which offers the potential to reuse components that have already been implemented, for the realization of new services.

Real-world information, knowledge and procedures after which information systems are modeled are... more Real-world information, knowledge and procedures after which information systems are modeled are generally of dynamic nature and subject to changes, due to the emergence of new requirements or revisions to initial specifications. E-government information systems (eGIS) present a higher degree of volatility in their environment, since requirement changes may stem from multiple sources, including legislation changes, organizational reforms, end-user needs, interoperability and distribution concerns etc. To this end, the design and implementation of eGIS must adhere to paradigms and practices that facilitate the accommodation of changes to the eGIS as they occur in the real world. In this work, we present a role-based model for designing and implementing eGIS that can dynamically accomodate changes, providing the necessary facilities for modeling multiple aspects of the same real-world entities and delivering context-specific behaviour.

Novel and intelligent visualization methods are being developed in order to accommodate user sea... more 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’ 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.

In the mobile and pervasive computing environment, software engineering should not treat diversi... more In the mobile and pervasive computing environment, software engineering should not treat diversity and mobility as problems to overcome, but seek methods of which it could take advantage instead. In these environments, the selection of purpose-oriented and timely information, tailored to user preferences and media characteristics will ensure an optimised information delivery. To this end, the context .the information that surrounds the human-computer interaction. plays a key role and is rapidly changing in mobile settings, and the understanding of it is indispensable for the application designers in order to choose, capture and exploit it. In this work, we present an architecture facilitating the collection of context information and its exploitation for optimized information delivery, within mobile and pervasive computing environments.