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In the recommender systems literature, it has been shown that, in addition to improving system effectiveness, explaining recommendations may increase user satisfaction, trust, persuasion and loyalty. In general, explanations focus on the filtering algorithms or the users and items involved in the generation of recommendations. However, on certain domains that are rich on user-generated textual content, it would be valuable to provide justifications of recommendations according to arguments that are explicit, underlying or related with the data used by the systems, e.g., the reasons for customers' opinions in reviews of e-commerce sites, and the requests and claims in citizens' proposals and debates of e-participation platforms. In this context, there is a need and challenging task to automatically extract and exploit the arguments given for and against evaluated items. We thus advocate to focus not only on user preferences and item features, but also on associated arguments. In other words, we propose to not only consider what is said about items, but also why it is said. Hence, arguments would not only be part of the recommendation explanations, but could also be used by the recommendation algorithms themselves. To this end, in this thesis, we propose to use argument mining techniques and tools that allow retrieving and relating argumentative information from textual content, and investigate recommendation methods that exploit that information before, during and after their filtering processes, The author thanks his supervisor Iván Cantador for his valuable support and guidance in defining this thesis project. The work is supported by the Spanish Ministry of Science and Innovation (PID2019-108965GB-I00) more...

© ACM 2000 This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in UMAP '20: Proceedings of the 28th ACM Conference on User Modeling, Adaptation and Personalization, https://doi.org/10.1145/3340631.3394882, Users from Location-Based Social Networks can be characterised by how and where they move. However, most of the works that exploit this type of information neglect either its sequential or its geographical properties. In this article, we focus on a specific family of recommender systems, those based on nearest neighbours; we define related users based on common check-ins and similar trajectories and analyse their effects on the recommendations. For this purpose, we use a real-world dataset and compare the performance on different dimensions against several state-of-the-art algorithms. The results show that better neighbours could be discovered with these approaches if we want to promote novel and diverse recommendations, This work has been funded by the Ministerio de Ciencia, Innovación y Universidades (reference TIN2016-80630-P) and by the European Social Fund (ESF), within the 2017 call for predoctoral contracts. The first author also acknowledges the Ministerio de Educación y Formación Profesional, within the 2019-2020 call for collaboration grants more...

© Owner/Author 2020. This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in EASE '20: Proceedings of the Evaluation and Assessment in Software Engineering, https://doi.org/10.1145/3383219.3383246, Modelling is a fundamental activity in software engineering, which is often performed in collaboration. For this purpose, on-line tools running on the cloud are frequently used. However, recent advances in Natural Language Processing have fostered the emergence of chatbots, which are increasingly used for all sorts of software engineering tasks, including modelling. To evaluate to what extent chatbots are suitable for collaborative modelling, we conducted an experimental study with 54 participants, to evaluate the usability of a modelling chatbot called SOCIO, comparing it with the on-line tool Creately. We employed a within-subjects cross-over design of 2 sequences and 2 periods. Usability was determined by attributes of efficiency, effectiveness, satisfaction and quality of the results. We found that SOCIO saved time and reduced communication effort over Creately. SOCIO satisfied users to a greater extent than Creately, while in effectiveness results were similar. With respect to diagram quality, SOCIO outperformed Creately in terms of precision, while solutions with Creately had better recall and perceived success. However, in terms of accuracy and error scores, both tools were similar, Work funded by the Spanish Ministry of Science (project MASSIVE, RTI2018-095255-B-I00) and the R&D programme of Madrid (project FORTE, P2018/TCS-4314) more...

In March 2020, due to the Covid19 pandemic, higher education had to switch from face-to-face to exclusively virtual mode overnight. In this unexpected scenario, supervisors also had to adapt the assessment procedures, including the exams. This caused a significant controversy, as, according to many students, supervisors were more concerned about how to prevent students from cheating, than actually measuring their learning. This paper introduces an experience that implemented several of the students' requests in an online exam and conducts a comprehensive analysis of students’ behavior according to the virtual learning environment records. Different existing software tools are used for the analysis, complemented with a Python application ad-hoc developed. The objective indicators gathered provide evidence that some students cheated and invite focusing on evidence-based assessment. more...

Trivial Compiler Equivalence (TCE) has been recently proposed as an effective technique to detect equivalences between programs, where two or more programs are equivalent if the compiler pro duces the same binary code. Mutation testing can greatly benefit from TCE as a way to reveal some equivalent and duplicate mu tants, which traditionally hinder the applicability of the technique. For instance, previous research has shown that about 28% of the mutants generated by traditional mutation operators in C programs can be removed using TCE. However, the effectiveness of TCE has not been assessed with class-level operators, where the percentage of equivalent mutants is known to be higher than when using tra ditional ones. In this paper, we present an empirical study on the effectiveness of TCE at identifying equivalent and duplicate mutants using C++ class operators. The results show that TCE is helpful to discard equivalent and duplicate mutants: 241 out of 1,987 (12%) in our study, including 189 out of 684 (27.6%) manually-identified equivalent mutants. Large differences were observed among the different case studies, especially in the detection rate of equivalent mutants, which ranged from 4% to 45%. Ministerio de Economía y Competitividad TIN2015-65845-C3-3-R (DarDos) Ministerio de Economía y Competitividad TIN2015-70560-R (BELI) more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in ACM International Conference Proceeding Series.13 September 2016, Article number a28, http://dx.doi.org/10.1145/2998626.2998646, Este artículo se centra en el potencial que ofrecen los relojes inteligentes o smartwatches como interventores en el proceso de auto-regulación emocional de personas con Trastorno del Espectro Autista (TEA). Partiendo de un modelo de asistencia en sus tareas de auto-regulación, el artículo revisa las principales ventajas de estos dispositivos en cuanto a: ubicuidad, sensores y posibilidades de interacción. Por otro lado, se discute la idoneidad de éstos para este tipo de asistencia, incluyendo estudios que han hecho uso de estos dispositivos con fines similares y la relación de esta idea con el área de computación afectiva. Finalmente, se propone una aproximación tecnológica la para auto-regulación emocional que usa smartwatches y aplica el modelo de intervención mencionado, This article adresses the potential of smartwatchers as interventors in the self-regulation process of individuals with ASD. We study an assistance model from the literature, and then we state some of the main features that lead us to this proposal: ubiquity, sensing and interaction possibilities. Also, we study the suitability of these devices, including previous work that have used them for assistive purposes. Finally, we propose a technologic approach for the emotional self-regulation that uses smartwatches and applies the mentioned model, Este trabajo ha sido financiado parcialmente por los proyectos: “e-Training y e-Coaching para la integración socio-laboral” (TIN2013-44586-R), “eMadrid-CM: Investigación y Desarrollo de Tecnologías en la Comunidad de Madrid” (S2013/ICE-2715) y la Fundación Orange, mediante el proyecto “Tic-Tac-TEA: Sistema de asistencia para la autorregulación emocional de momentos de crisis para personas con TEA mediante smartwatches" more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in SLE 2015: Proceedings of the 2015 ACM SIGPLAN International Conference on Software Language Engineering, http://dx.doi.org/10.1145/10.1145/2814251.2814256, The definition of Domain-Specific Languages (DSLs) is a recurrent activity in Model-Driven Engineering. However, their construction is many times an ad-hoc process, partly due to the lack of tools enabling a proper engineering of DSLs and promoting domain experts to play an active role. The focus of this paper is on the validation of meta- models for visual DSLs. For this purpose, we propose a language and tool support for describing properties that in- stances of meta-models should (or should not) meet. Then, our system uses a model finder to produce example models, enriched with a graphical concrete syntax, that confirm or refute the assumptions of the meta-model developer. Our language complements metaBest, a framework for the validation and verification of meta-models that includes two other languages for unit testing and specification-based test- ing of meta-models. A salient feature of our approach is that it fosters interaction with domain experts by the use, process- ing and creation of informal drawings constructed in editors liked yED or Dia. We assess the usefulness of the approach in the validation of a DSL for house blueprints, with the par- ticipation of 26 4th year computer science students., Work supported by the Spanish MINECO (TIN2011-24139 and TIN2014-52129-R), the R&D programme of the Madrid Region (S2013/ICE-3006), and the EU commission (FP7-ICT-2013-10, #611125). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Interacción '15: Proceedings of the XVI International Conference on Human Computer Interaction, http://dx.doi.org/10.1145/2829875.2829919., For the most part, Information Architecture processes include sets of activities and techniques to be carried out by the development team to create interactive applications effectively, involving usability concerns at every development step. In fact, plenty of process models have already been proposed to bridge the gap between User-Centered Development and Information Architecture, empowering the development team to build usable applications successfully. However, the combination of User- Centered Development and Information Architecture paradigms sometimes results in cumbersome process models containing lots of phases and activities to be considered, which increases the cycle time to have partial and validated software increments readily. As less effort has been devoted to speed up the usable Information Architecture development, the aim of this paper is to address such problem. To do so, we present Scrum-UIA, an agile and usable development process driven by the Information Architecture. This process is intended to develop web applications by splitting up responsibilities and tasks, and decreasing the time to perform technical activities, in order to readily obtain usable software increments., This work has been supported by the funding projects «eMadrid», granted by the Madrid Research Council (project code S2013/ICE-2715) and «Flexor», granted by the Spanish Government (project code TIN2014-52129-R). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in RecSys '14 Proceedings of the 8th ACM Conference on Recommender systems, http://dx.doi.org/10.1145/2645710.2645746, Recommender systems research is often based on comparisons of predictive accuracy: the better the evaluation scores, the better the recommender. However, it is difficult to compare results from different recommender systems due to the many options in design and implementation of an evaluation strategy. Additionally, algorithmic implementations can diverge from the standard formulation due to manual tuning and modifications that work better in some situations. In this work we compare common recommendation algorithms as implemented in three popular recommendation frameworks. To provide a fair comparison, we have complete control of the evaluation dimensions being benchmarked: dataset, data splitting, evaluation strategies, and metrics. We also include results using the internal evaluation mechanisms of these frameworks. Our analysis points to large differences in recommendation accuracy across frameworks and strategies, i.e. the same baselines may perform orders of magnitude better or worse across frameworks. Our results show the necessity of clear guidelines when reporting evaluation of recommender systems to ensure reproducibility and comparison of results., This work was partly carried out during the tenure of an ERCIM “Alain Bensoussan” Fellowship Programme. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreements n◦246016 and n◦610594, and the Spanish Ministry of Science and Innovation (TIN2013-47090-C3-2) more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 7th ACM international conference on Web search and data mining, http://dx.doi.org/10.1145/2556195.2556199, This tutorial aims to provide a unifying account of current research on diversity and novelty in the domains of web search, recommender systems, and data stream processing. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in RecSys '13 Proceedings of the 7th ACM conference on Recommender systems, http://dx.doi.org/10.1145/2507157.2508006., Experiment replication and reproduction are key requirements for empirical research methodology, and an important open issue in the field of Recommender Systems. When an experiment is repeated by a different researcher and exactly the same result is obtained, we can say the experiment has been replicated. When the results are not exactly the same but the conclusions are compatible with the prior ones, we have a reproduction of the experiment. Reproducibility and replication involve recommendation algorithm implementations, experimental protocols, and evaluation metrics. While the problem of reproducibility and replication has been recognized in the Recommender Systems community, the need for a clear solution remains largely unmet, which motivates the present workshop., This workshop was carried out during the tenure of an ERCIM “Alain Bensoussan” Fellowship Programme, funded by European Comission FP7 grant agreement no.246016. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in CIKM '12 Proceedings of the 21st ACM international conference on Information and knowledge management, http://dx.doi.org/10.1145/2396761.2398628., Popular online rental services such as Netflix and MoviePilot often manage household accounts. A household account is usually shared by various users who live in the same house, but in general does not provide a mechanism by which current active users are identified, and thus leads to considerable difficulties for making effective personalized recommendations. The identification of the active household members, defined as the discrimination of the users from a given household who are interacting with a system (e.g. an on-demand video service), is thus an interesting challenge for the recommender systems research community. In this paper, we formulate the above task as a classification problem, and address it by means of global and local feature selection methods and classifiers that only exploit time features from past item consumption records. The results obtained from a series of experiments on a real dataset show that some of the proposed methods are able to select relevant time features, which allow simple classifiers to accurately identify active members of household accounts., This work was supported by the Spanish Government (TIN2011-28538-C02). The authors thank Centro de Computación Científica at UAM for its technical support. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in SIGIR '12 Proceedings of the 35th international ACM SIGIR conference on Research and development in information retrieval, http://dx.doi.org/10.1145/2348283.2348297., The intent-oriented search diversification methods developed in the field so far tend to build on generative views of the retrieval system to be diversified. Core algorithm components in particular redundancy assessment are expressed in terms of the probability to observe documents, rather than the probability that the documents be relevant. This has been sometimes described as a view considering the selection of a single document in the underlying task model. In this paper we propose an alternative formulation of aspect-based diversification algorithms which explicitly includes a formal relevance model. We develop means for the effective computation of the new formulation, and we test the resulting algorithm empirically. We report experiments on search and recommendation tasks showing competitive or better performance than the original diversification algorithms. The relevance-based formulation has further interesting properties, such as unifying two well-known state of the art algorithms into a single version. The relevance-based approach opens alternative possibilities for further formal connections and developments as natural extensions of the framework. We illustrate this by modeling tolerance to redundancy as an explicit configurable parameter, which can be set to better suit the characteristics of the IR task, or the evaluation metrics, as we illustrate empirically., This work was supported by the national Spanish projects TIN2011-28538-C02-01 and S2009TIC-1542. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 4th International Workshop on Web Intelligence & Communities, http://dx.doi.org/10.1145/2189736.2189743, Virtual Worlds (VWs) platforms and applications provide a practical implementation of the Metaverse concept. These applications, as highly inmersive and interactive 3D environments, have become very popular in social networks and games domains. The existence of a set of open platforms like OpenSim or OpenCobalt have played a major role in the popularization of this technology and they open new exciting research areas. One of these areas is behaviour analysis. In virtual world, the user (or avatar) can move and interact within an artificial world with a high degree of freedom. The movements and iterations of the avatar can be monitorized, and hence this information can be analysed to obtain interesting behavioural patterns. Usually, only the information related to the avatars conversations (textual chat logs) are directly available for processing. However, these open platforms allow to capture other kind of information like the exact position of an avatar in the VW, what they are looking at (eye-gazing) or which actions they perform inside these worlds. This paper studies how this information, can be extracted, processed and later used by clustering methods to detect behaviour or group formations in the world. To detect the behavioural patterns of the avatars considered, clustering techniques have been used. These techniques, using the correct data preprocessing and modelling, can be used to automatically detect hidden patterns from data., This work has been partly supported by: Spanish Ministry of Science and Education under the project TIN2010-19872 more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 6th International Workshop on Multi-Paradigm Modeling, http://dx.doi.org/10.1145/2508443.2508449, Complex systems require descriptions using multiple modelling languages, or languages able to express different concerns, like timing or data dependencies. In this paper, we propose techniques for the modular definition and composition of languages, including their abstract, concrete syntax and semantics. These techniques are based on (meta-)model templates, where interface elements and requirements for their connection can be established. We illustrate the ideas using the MetaDepth textual meta-modelling tool. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in CIKM '12 Proceedings of the 21st ACM international conference on Information and knowledge management, http://dx.doi.org/10.1145/2396761.2398760., This paper provides an overview of the 1st International Workshop on Multimodal Crowd Sensing (CrowdSens 2012), held at the 21st ACM International Conference on Information and Knowledge Management (CIKM 2012). This workshop aimed to provide an open forum for researchers from various fields such as fields such as Natural Language Processing, Information Extraction, Data Mining, Information Retrieval, User Modeling and Personalization, Stream Processing, and Sensor Networks, for addressing the challenges of effectively mining, analyzing, fusing, and exploiting information sourced from multimodal physical and social sensor data sources., We thank the EU-FP7 project WeGov (grant 248512), and the Spanish project i3media (CENIT-2007-1012) for sponsoring the workshop. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in RecSys '10 Proceedings of the fourth ACM conference on Recommender systems, http://dx.doi.org/10.1145/1864708.1864796., There is considerable methodological divergence in the way precision-oriented metrics are being applied in the Recommender Systems field, and as a consequence, the results reported in different studies are difficult to put in context and compare. We aim to identify the involved methodological design alternatives, and their effect on the resulting measurements, with a view to assessing their suitability, advantages, and potential shortcomings. We compare five experimental methodologies, broadly covering the variants reported in the literature. In our experiments with three state-of-the-art recommenders, four of the evaluation methodologies are consistent with each other and differ from error metrics, in terms of the comparative recommenders' performance measurements. The other procedure aligns with RMSE, but shows a heavy bias towards known relevant items, considerably overestimating performance., This work was supported by the Spanish Ministry of Science and Innovation (TIN2008-06566-C04-02) and the Community of Madrid (CCG10-UAM/TIC-5877) more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in WIMS '11 Proceedings of the International Conference on Web Intelligence, Mining and Semantics, http://dx.doi.org/10.1145/1988688.1988718., The Eurovision contest has been the reference on european song contests for the past 50 years. Countries in the European Union can shows the rest of the participants their current music tendencies. This phenomena has been studied in domains like physic and social sciences to find correlations between contests and current political and socio-economy trends in EU. The inclusion of web and social technologies some years ago, have caused a disruption in the traditional voting system whereby the audience is encouraged to participate by casting votes for their favorite song. As a result, this system yields new, relevant information that may be extrapolated to social and political tendencies in Europe with a higher degree accuracy than by data collected using the previous jury-based system. This paper provides an initial data analysis in crowd behavior to assess the impact of the televote system, in the Eurovision voting dynamic, by focusing on two distinct five years periods that can successfully contrast each voting scheme. Analyzing these periods separately, we can observe results from the televoting contests and then compare to the jury to see if there is a change in voting patterns. Finally, we study the underlying community structure of the voting network using the Cluster Percolation Method and Edge Betweenness to discover stable core communities spanning a number of years in the contest. The clusters obtained using these algorithms are then used to compare how these stable communities have evolving during the considered periods., This work has been funded by the Spanish Ministry of Science and Technology under the projects ABANT (TIN2010 19872) more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 34th international ACM SIGIR conference on Research and development in Information Retrieval, http://dx.doi.org/10.1145/2009916.2010092, Ensemble recommender systems successfully enhance recom-mendation accuracy by exploiting different sources of user prefe-rences, such as ratings and social contacts. In linear ensembles, the optimal weight of each recommender strategy is commonly tuned empirically, with limited guarantee that such weights are optimal afterwards. We propose a self-adjusting hybrid recommendation approach that alleviates the social cold start situation by weighting the recommender combination dynamically at recommendation time, based on social network analysis algorithms. We show empirical results where our approach outperforms the best static combination for different hybrid recommenders., This work was supported by the Spanish Ministry of Science and Innovation (TIN2008-06566-C04-02), University Autónoma de Madrid and the Community of Madrid (CCG10-UAM/TIC-5877). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in roceedings of the 34th international ACM SIGIR conference on Research and development in Information Retrieval, http://dx.doi.org/10.1145/2009916.2010097, Diversification and personalization methods are common ap-proaches to deal with the one-size-fits-all paradigm of Web search engines. We performed a user study with 190 subjects where we analyzed the effects of diversification and personalization methods in a Web search engine. The obtained results suggest that our proposed combination of diversification and personalization factors may be a way to overcome the notion of intrusiveness in personalized approaches., This work is supported by the Spanish Government (TIN2008-06566-C04-02), and the Government of Madrid (S2009TIC-1542). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 34th international ACM SIGIR conference on Research and development in Information Retrieval, http://dx.doi.org/10.1145/2009916.2010124., Diversity as a relevant dimension of retrieval quality is receiving increasing attention in the Information Retrieval and Recommender Systems (RS) fields. The problem has nonetheless been approached under different views and formulations in IR and RS respectively, giving rise to different models, methodologies, and metrics, with little convergence between both fields. In this poster we explore the adaptation of diversity metrics, techniques, and principles from ad-hoc IR to the recommendation task, by introducing the notion of user profile aspect as an analogue of query intent. As a particular approach, user aspects are automatically extracted from latent item features. Empirical results support the proposed approach and provide further insights., This work is supported by the Spanish Government (TIN2008- 06566-C04-02), and the Government of Madrid (S2009TIC-1542). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in RecSys '11 Proceedings of the fifth ACM conference on Recommender systems, http://dx.doi.org/10.1145/2043932.2044016. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in RecSys '11 Proceedings of the fifth ACM conference on Recommender systems, http://dx.doi.org/10.1145/2043932.2043955, The Recommender Systems community is paying increasing attention to novelty and diversity as key qualities beyond accuracy in real recommendation scenarios. Despite the raise of interest and work on the topic in recent years, we find that a clear common methodological and conceptual ground for the evaluation of these dimensions is still to be consolidated. Different evaluation metrics have been reported in the literature but the precise relation, distinction or equivalence between them has not been explicitly studied. Furthermore, the metrics reported so far miss important properties such as taking into consideration the ranking of recommended items, or whether items are relevant or not, when assessing the novelty and diversity of recommendations. We present a formal framework for the definition of novelty and diversity metrics that unifies and generalizes several state of the art metrics. We identify three essential ground concepts at the roots of novelty and diversity: choice, discovery and relevance, upon which the framework is built. Item rank and relevance are introduced through a probabilistic recommendation browsing model, building upon the same three basic concepts. Based on the combination of ground elements, and the assumptions of the browsing model, different metrics and variants unfold. We report experimental observations which validate and illustrate the properties of the proposed metrics., This work is supported by the Spanish Government (TIN2011- 28538-C02-01), and the Government of Madrid (S2009TIC-1542). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 19th ACM international conference on Multimedia, http://dx.doi.org/10.1145/2072298.2072401, This short overview describes the contents of the tutorial Semantic computing in multimedia, which was offered to the participants of ACM Multimedia 2011. Given the impossibility of summarizing properly the contents of the tutorial in just two pages, the purpose of this overview is mainly to introduce the reader to the relevant bibliography. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in RecSys '11 Proceedings of the fifth ACM conference on Recommender systems, http://dx.doi.org/10.1145/2043932.2043990., The use of temporal dynamic terms in Matrix Factorization (MF) models of recommendation have been proposed as a means to obtain better accuracy in rating prediction task. However, the way such models have been tested may not be a realistic setting for recommendation. In this paper, we evaluated rating prediction and top-N recommendation tasks using a MF model with and without temporal dynamic terms under two evaluation settings. Our experiments show that the addition of dynamic parameters do not necessarily yield to better results on these tasks when a more strict time-aware separation of train/test data is performed, and moreover, results may vary notably when different evaluation schemes are used., This work is supported by the Spanish Government (TIN 2008-06566-C04-02) and by the Comunidad de Madrid and Universidad Autónoma de Madrid (CCG10-UAM/TIC-5877). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in CAMRa '11 Proceedings of the 2nd Challenge on Context-Aware Movie Recommendation, http://dx.doi.org/10.1145/2096112.2096118., In this paper, we describe the experiments conducted by the Information Retrieval Group at the Universidad Autónoma de Madrid (Spain) to tackle the Identifying Ratings (track 2) task of the CAMRa 2011 Challenge. The experiments performed include time-frequency probabilistic strategies, heuristic collaborative filtering (CF) and a model-based CF approach. Results show that probabilistic classifiers based on temporal behavior of users have better performance than traditional recommendation-based strategies, thus reflecting that temporal information is a valuable source for the identification or discrimination of user ratings., This work is supported by the Spanish Government (TIN 2008-06566-C04-02) and by the Comunidad de Madrid and Universidad Aut´onoma de Madrid (CCG10-UAM/TIC-5877). The authors acknowledge support from CCC at UAM. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in CIKM '11 Proceedings of the 20th ACM international conference on Information and knowledge management, http://dx.doi.org/10.1145/10.1145/2063576.2063940., In a general collaborative filtering (CF) setting, a user profile contains a set of previously rated items and is used to represent the user's interest. Unfortunately, most CF approaches ignore the underlying structure of user profiles. In this paper, we argue that a certain class of interest is best represented jointly by several items, drawing an analogy to "phrases" in text retrieval, which are not equivalent to the separate meaning of their words. At an alternative stance, we also consider the situation where, analogously to word synonyms, two items might be substitutable when representing a class of interest. We propose an approach integrating these two notions as opposing poles on a continuum spectrum. Upon this, we model the underlying structure in user profiles, drawing an analogy with text retrieval. The approach gives rise to a novel structured Vector Space Model for CF. We show that item-based CF approaches are a special case of the proposed method., This work was supported by the Spanish Ministry of Science and Innovation (TIN2008-06566-C04-02), University Aut´onoma de Madrid and the Community of Madrid (CCG10- -UAM/TIC-5877). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in RecSys '10 Proceedings of the fourth ACM conference on Recommender systems , http://dx.doi.org/10.1145/10.1145/1864708.1864756., In a general collaborative filtering (CF) setting, a user profile contains a set of previously rated items and is used to represent the user's interest. Unfortunately, most CF approaches ignore the underlying structure of user profiles. In this paper, we argue that a certain class of interest is best represented jointly by several items, drawing an analogy to "phrases" in text retrieval, which are not equivalent to the separate meaning of their words. At an alternative stance, we also consider the situation where, analogously to word synonyms, two items might be substitutable when representing a class of interest. We propose an approach integrating these two notions as opposing poles on a continuum spectrum. Upon this, we model the underlying structure in user profiles, drawing an analogy with text retrieval. The approach gives rise to a novel structured Vector Space Model for CF. We show that item-based CF approaches are a special case of the proposed method. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 12th annual conference on Genetic and evolutionary computation , http://dx.doi.org/10.1145/1830483.1830657, Success Rate (SR) is a statistic straightforward to use and interpret, however a number of non-trivial statistical issues arises when it is examinated in detail. We address some of those issues, providing evidence that suggests that SR follows a binomial density function, therefore its statistical properties are independent of the flavour of the Evolutionary Algorithm (EA) and its domain. It is fully described by the SR and the number of runs. Moreover, the binomial distribution is a well known statistical distribution with a large corpus of tools available that can be used in the context of EC research. One of those tools, confidence intervals (CIs), is studied more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 21st ACM conference on Hypertext and hypermedia, http://dx.doi.org/10.1145/1810617.1810657, Adaptive link annotation is one of the most popular adaptive educational hypermedia techniques. It has been widely studied and demonstrated its ability to help students to acquire knowledge faster, improve learning outcomes, reduce navigation overhead, increase motivation, and encourage the beneficial non-sequential navigation. However, almost all studies of adaptive link annotation have been performed in the context of dedicated adaptive educational hypermedia systems. The role of this technique in the context of widely popular learning portals has not yet been demonstrated. In this paper, we attempt to fill this gap by investigating the value of adaptive navigation support embedded into the learning portal. We compare the effect of portal-based adaptive navigation support to both the effect of the adaptive navigation support in adaptive educational hypermedia systems and to non-adaptive learning portals., This work is supported by National Science Foundation under Grant IIS-0447083, Spanish Ministry of Science and Education (TIN2007-64718) and the Comunidad Autónoma de Madrid (S2009/TIC-1650) more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 33rd international ACM SIGIR conference on Research and development in information retrieval, http://dx.doi.org/10.1145/1835449.1835636, In this paper, we present a folksonomy-based approach for implicit user intent extraction during a Web search process. We present a number of result re-ranking techniques based on this representation that can be applied to any Web search engine. We perform a user experiment the results of which indicate that this type of representation is better at context extraction than using the actual textual content of the document., This research was partially supported by the Spanish Ministry of Science and Education (TIN2008-06566-C04-02) and the Regional Government of Madrid (S2009TIC-1542). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in MIR '10 Proceedings of the international conference on Multimedia information retrieval, http://dx.doi.org/10.1145/1743384.1743406 ., Most video retrieval systems are multimodal, commonly relying on textual information, low- and high-level semantic features extracted from query visual examples. In this work, we study the impact of exploiting different knowledge sources in order to automatically retrieve query visual examples relevant to a video retrieval task. Our hypothesis is that the exploitation of external knowledge sources can help on the identification of query semantics as well as on improving the understanding of video contents. We propose a set of techniques to automatically obtain additional query visual examples from different external knowledge sources, such as DBPedia, Flickr and Google Images, which have different coverage and structure characteristics. The proposed strategies attempt to exploit the semantics underlying the above knowledge sources to reduce the ambiguity of the query, and to focus the scope of the image searches in the repositories. We assess and compare the quality of the images obtained from the different external knowledge sources when used as input of a number of video retrieval tasks. We also study how much they complement manually provided sets of examples, such as those given by TRECVid tasks. Based on our experimental results, we report which external knowledge source is more likely to be suitable for the evaluated retrieval tasks. Results also demonstrate that the use of external knowledge can be a good complement to manually provided examples and, when lacking of visual examples provided by a user, our proposed approaches can retrieve visual examples to improve the user's query., This research was supported by the European Commission under contract FP6-027122-SALERO and by the Spanish Ministry of Science and Education (TIN2008-06566- C04-02). more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in CAMRa '10 Proceedings of the Workshop on Context-Aware Movie Recommendation, http://dx.doi.org/10.1145/1869652.1869660, In this paper, we describe the experiments conducted by the Information Retrieval Group at the Universidad Autónoma de Madrid (Spain) in order to better recommend movies for the 2010 CAMRa Challenge edition. Experiments were carried out on the dataset corresponding to social Filmtipset track. To obtain the movies recommendations we have used different algorithms based on Random Walks, which are well documented in the literature of collaborative recommendation. We have also included a new proposal in one of the algorithms in order to get better results. The results obtained have been computed by means of the trec_eval standard NIST evaluation procedure., This research was supported by the Spanish Ministry of Science and Innovation (TIN2008-06566-C04-02) and the Scientific Computing Institute at UAM. The third author also wants to acknowledge support from the Chilean Government through the Becas-Chile scholarship program more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in CAMRa '10 Proceedings of the Workshop on Context-Aware Movie Recommendation, http://dx.doi.org/10.1145/1869652.1869655., In this paper, we describe the experiments conducted by the Information Retrieval Group at the Universidad Autónoma de Madrid (Spain) in order to better recommend movies for the 2010 CAMRa Challenge edition. Experiments were carried out on the dataset corresponding to weekly Filmtipset track. We consider simple strategies for taking into account the temporal context for movie recommendations, mainly based on variations of the KNN algorithm, which has been deeply studied in the literature, and one ad-hoc strategy, taking advantage of particular information in the weekly Filmtipset track. Results show that the usage of information near to the recommendation date alone can help improving recommendation results, with the additional benefit of reducing the information overload of the recommender engine. Furthermore, the use of social interaction information shows also a contribution in order to better predict a part of users' tastes., This research was supported by the Spanish Ministry of Science and Innovation (TIN2008-06566-C04-02) and the Scientific Computing Institute at UAM. The first author acknowledges support from the Chilean Government through the Becas-Chile scholarship program more...

1. MOTIVATION AND GOALS In recent years, increasing attention has been given to finding ways for combining, integrating and mediating heterogeneous sources of information for the purpose of providing better personalized services in many information seeking and ecommerce applications. Information heterogeneity can indeed be identified in any of the pillars of a recommender system: the modeling of user preferences, the description of resource contents, the modeling and exploitation of the context in which recommendations are made, and the characteristics of the suggested resource lists. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 2nd ACM SIGCHI symposium on Engineering interactive computing systems, http://dx.doi.org/10.1145/1822018.1822047, Querying databases is a common daily task carried out by a great deal of end-users who do not have specific skills in SQL language. Today, most of the database interaction is achieved by means of query interfaces provided by the database environment. However, most of these interfaces suffer from expressive limitations, since they are mostly based on metaphors that drastically restrict the expressiveness of the SQL language that is generated and executed in the background. In this paper, we present a visual interaction language and tool focused on easily querying databases by end-users. We make no assumption on the level of the user's experience with query languages, as our visual metaphor is intended for querying databases by unskilled end-users and also leveraging the restriction on the expressiveness of the queries created by them. We also report on some late braking results obtained by an experiment carried out with real users., The work reported in this paper is being partially supported by the founded projects TIN2008-02081/TIN and S2009/TIC-1650. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in HT '08 Proceedings of the nineteenth ACM conference on Hypertext and hypermedia, http://dx.doi.org/10.1145/1379092.1379103., As the popularity of the web increases, particularly the use of social networking sites and style sharing platforms, users are becoming increasingly connected, sharing more and more information, resources, and opinions. This vast array of information presents unique opportunities to harvest knowledge about user activities and interests through the exploitation of large-scale, complex systems. Communal tagging sites, and their respective folksonomies, are one example of such a complex system, providing huge amounts of information about users, spanning multiple domains of interest. However, the current Web infrastructure provides no mechanism for users to consolidate and exploit this information since it is spread over many desperate and unconnected resources. In this paper we compare user tag-clouds from multiple folksonomies to: (a) show how they tend to overlap, regardless of the focus of the folksonomy (b) demonstrate how this comparison helps finding and aligning the user's separate identities, and (c) show that cross-linking distributed user tag-clouds enriches users profiles. During this process, we find that significant user interests are often reflected in multiple Web2.0 profiles, even though they may operate over different domains. However, due to the free-form nature of tagging, some correlations are lost, a problem we address through the implementation and evaluation of a user tag filtering architecture., This research has been supported by the TAGora project, funded by the Future and Emerging Technologies program (IST-FET) of the European Commission under the contract IST-34721, and the Spanish Ministry of Science and Education (TIN2005–6885). The information provided is the sole responsibility of the authors and does not reflect the Commission’s opinion. The Commission is not responsible for any use that may be made of data appearing in this publication. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in ICML '06 Proceedings of the 23rd international conference on Machine learning, http://dx.doi.org/10.1145/1143844.1143921, We present a novel ensemble pruning method based on reordering the classifiers obtained from bagging and then selecting a subset for aggregation. Ordering the classifiers generated in bagging makes it possible to build subensembles of increasing size by including first those classifiers that are expected to perform best when aggregated. Ensemble pruning is achieved by halting the aggregation process before all the classifiers generated are included into the ensemble. Pruned subensembles containing between 15% and 30% of the initial pool of classifiers, besides being smaller, improve the generalization performance of the full bagging ensemble in the classification problems investigated., The authors acknowledge financial support from the Spanish Dirección General de Investigación, project TIN2004-07676-C02-02. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the 7th annual conference on Genetic and evolutionary computation, http://dx.doi.org/10.1145/1068009.1068317, Constructive Induction is the process of transforming the original representation of hard concepts with complex interaction into a representation that highlights regularities. Most Constructive Induction methods apply a greedy strategy to find interacting attributes and then construct functions over them. This approach fails when complex interaction exists among attributes and the search space has high variation. In this paper, we illustrate the importance of applying Genetic Algorithms as a global search strategy for these methods and present MFE2/GA1, while comparing it with other GA-based Constructive Induction methods. We empirically analyze our Genetic Algorithm's operators and compare MFE2/GA with greedy-based methods. We also performed experiments to evaluate the presented method when concept has attributes participating in more than one complex interaction. In experiments that are conducted, MFE2/GA successfully finds interacting attributes and constructs functions to represent interactions. Results show the advantage of using Genetic Algorithms for Constructive Induction when compared with greedy-based methods., This work has been partially supported by the Spanish Ministry of Science and Technology, under grant number TIC2002-1948 more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in CompSysTech '03 Proceedings of the 4th international conference conference on Computer systems and technologies: e-Learning, http://dx.doi.org/10.1145/973620.973661., Natural images form very small subset of all images. In spite of the fact, the direct computation of their block densities is not possible. On the other hand, the existence of various successful image compression methods, in particularly, the fractal compression, indicates that the compression somehow is able to capture and use at least part of the natural image statistics. In this work we show how hash based fractal image compression can be used to derive quite precise the entropies of 4 × 4 patches of the natural images. We state that the probability density in first order factorize to the probability densities of the contrast, the brightness and the index of the codebook blocks. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in APL Quote Quad, http://dx.doi.org/10.1145/604444.602249, Proceedings of the 2002 conference on APL: array processing languages: lore, problems, and applications (Madrid), This work describes how grammatical evolution may be applied to the domain of automatic composition. Our goal is to test this technique as an alternate tool for automatic composition. The AP440 auxiliary processor will be used to play music, thus we shall use a grammar that generates AP440 melodies. Grammar evolution will use fitness functions defined from several well-known single melodies to automatically generate AP440 compositions that are expected to sound like those composed by human musicians., This paper has been sponsored by the Spanish Interdepartmental Commission of Science and Technology (CICYT), project numbers TEL1999-0181 and TIC2001-0685-C02-1. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in APL Quote Quad 32.4 (2002): 17 – 26, http://dx.doi.org/10.1145/604444.602233, We have been working for several years on the representation, study and simulation of complex systems by means of formal methods. APL2 and other programming languages have been used to develop our tools and experiments. This paper summarizes our APL2 works on fractal sets, automatic programming of cellular automata and simulation of multi agent systems ., This paper has been sponsored by the Spanish Interdepartmental Commission of Science and Technology (CICYT), project numbers TEL1999-0181 and TIC2001-4937-E. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in APL Quote Quad, http://dx.doi.org/10.1145/570440.570477, In this paper we describe the use of APL2 to implement and depict the equivalence between the mathematical field of fractal curves and the linguistic field of parallel derivation grammars, by tackling the problem of determining the dimension of a fractal from its representation as a grammar. APL2 makes the required computation quite easy., This paper has been sponsored by the Spanish Interdepartmental Commission of Science and Technology (CICYT), project numbers TEL1999-0181 and TEL97- 0306. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in APL Quote Quad, http://dx.doi.org/10.1145/327600.327644, This paper describes the procedure used to build several courses on the sciences for the high school level. An APL2 program has been written that accepts problem models, including explanation models, and uses them to generate many different problems. Each course is provided with about one hundred problem models, from which the student is invited to solve many thousands of different actual problems. The unique features of APL2 have made it very simple to develop the program that supports the courses, which exists in both DOS and Windows versions. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in IUI '97 Proceedings of the 2nd international conference on Intelligent user interfaces, http://dx.doi.org/10.1145/238218.238315., Current interface development tools cannot be used to specify complex displays without resorting to programming using a toolkit or graphics package. Interface builders and multi-media authoring tools only support the construction of static displays where the components of the display are known at design time (e.g., buttons, menus). This paper describes a presentation modeling system where complex displays of dynamically changing data can be modeled declaratively. The system incorporates principles of graphic design such as guides and grids, supports constraint-based layout and automatic update when data changes, has facilities for easily specifying the layout of collections of data, and has facilities for making displays sensitive to the characteristics of the data being presented and the presentation context (e.g., amount of space available). Finally, the models are designed to be amenable to interactive specification and specification using demonstrational techniques. more...

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in APL Quote Quad, http://dx.doi.org/10.1145/253417.253348, Proceedings of the conference on Designing the future, APL'96; published as an article, Fractals can be represented by means of L-systems (Development Grammars), together with a graphic interpretation. Two families of graphic interpretations have been used: turtle graphics and vector graphics. This paper describes an APL2/PC system able to draw fractals represented by L-systems, with both graphic interpretations. A theorem has been proved on the equivalence conditions for both interpretations. Another point shown is the fact that supposed deficiencies in L-systems that have prompted proposals of extensions are really deficiencies in the graphic translation scheme. more...