@conference {873,
	title = {Optimizing Collaborative Filtering in Very Sparse Datasets: a Confidence-based Approach},
	booktitle = {Proceedings of the 2026 International Conference on Information, Intelligence, Systems and Applications},
	year = {2026},
	publisher = {IEEE Xplore},
	organization = {IEEE Xplore},
	abstract = {<p>Collaborative filtering systems are a key tool for personalized recommendations, predicting user preferences based on historical data. A major challenge in collaborative filtering is the reliability of predictions, particularly in highly sparse datasets, where the limited overlap of common ratings between users impedes the identification of reliable neighbors, reducing both the accuracy and coverage of the predictions. So far, the literature has proposed confidence factors to quantify prediction reliability, typically using the Pearson and Cosine similarities with threshold-based neighbor selection. However, a recent study demonstrated that using the Sigmoid Cosine similarity metric in combination with the KNN neighborhood selection method and adapting the value of K to each level of dataset sparsity, significantly improves prediction performance. In this paper, we revisit the calculation of confidence factors under these improved settings, assessing their validity and effectiveness across datasets with varying sparsity levels. Continuous assessment of collaborative filtering methods and adjustment of their parameters according to dataset characteristics is particularly crucial in highly sparse datasets, where the reliability of neighbors strongly influences prediction quality.</p>
},
	keywords = {collaborative filtering, Confidence Factors, Optimization, Rating Predictions, Recommender Systems, Sparse Datasets},
	author = {Vassiliki Stouraiti and Giorgos Mpardis and Konstantinos I. Roumeliotis and Costas Vassilakis and Christos Tryfonopoulos and Dimitris Spiliotopoulos}
}
@conference {Vassilakis20071564,
	title = {Web service execution streamlining},
	booktitle = {Proceedings - ICSSSM{\textquoteright}06: 2006 International Conference on Service Systems and Service Management},
	volume = {2},
	year = {2007},
	note = {cited By (since 1996) 0},
	month = {10},
	pages = {1564-1569},
	abstract = {Web services are functional, independent components that can be called over the web to perform a task. Besides being used individually to deliver some well-specified functionality, web services may be used as building blocks that can be combined to implement a more complex function. In such compositions, typically some web services produce results that are used as input for web services that will be subsequently invoked. In the execution schemes currently employed, web services producing intermediate results deliver them to some "coordinating entity", which arranges the forwarding of these intermediate results to web services that require them as input. In this paper we present an execution scheme that employs direct communication between producers and consumers of intermediate results. Besides performance improvement stemming from reduction of network communication, this scheme permits consumer web services to employ simpler authenticity and integrity verification algorithms on incoming parameters. when the producer web service is considered trustworthy. Β{\textcopyright}2006 IEEE.},
	keywords = {Algorithms, Function evaluation, Optimization, Parameter estimation, Streamlining, Web service execution, Web service synthesis, Web services},
	doi = {10.1109/ICSSSM.2006.320769},
	url = {http://ieeexplore.ieee.org/document/4114724/},
	author = {Costas Vassilakis and Giorgos Lepouras and Akrivi Katifori}
}
@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}
}
