1,721,012 research outputs found
Designing Ontology-Based Data Access Solutions: Representation and Reasoning Support
No full textWhile OBDA has been the focus of many different studies in recent years, these studies typically have focused on the core aspects of OBDA, in particular on query answering. Less attention, in this context, has been dedicated to other aspects such as ontology representation, ontology visualization, and intentional reasoning. From the experience matured in the last few years in working with OBDA, it is clear that these problems, while also representing independent research fields, all play a significant part in the construction of the architecture of a full-fledged OBDA system, and therefore must be addressed. Unfortunately, the results that are found in literature regarding these issues are unsatisfactory when taken in the context of OBDA, because they are not tailored towards the languages and the applications that are adopted under the OBDA framework. This thesis addresses these issues and presents solutions for them in the context of the OBDA framework. The integration of these solutions and techniques into an OBDA system allows to provide users with full support for all
OBDA-related activities. We briefly summarize in the following the main contributions provided in this thesis: we present the novel Graphol language for the graphical specification of DL ontologies; we study the problem of approximating DL ontologies specified in an expressive source language in terms of less expressive target languages; we deal with core intentional reasoning services over an ontology, devising efficient methods and implementations that are specifically tailored towards languages that are suitable for OBDA
Towards efficient and practical solutions for ontology-based data management
No full textThis paper presents the research summary of my Ph.D. plan, which is currently in the early stages of its development. The objectives around which my work is focusing and that I will continue to pursue throughout the remainder of my doctoral activities are the development of tools and the definition of a methodology for the execution of those tasks that are typically performed when working with ontologies in the context of Ontology-Based Data Access (OBDA). The objective of this methodology is to guide the ontology engineer through ontology design, representation and approximation, and the issues I will address in order to provide the necessary tools to achieve this goal are the optimization of ontology classification in DL-Lite, the definition of a graphical language tailored towards ontologies, and the study of approximation of ontologies in expressive languages into DL-Lite logics. Such methodology proves to be necessary when facing the numerous challenges that often arise in real-world scenarios, in which the amount of data that is managed by information systems, and the processes that manage and act on this data grow continuously. © 2013 ACM
Graph-based ontology classification in OWL 2 QL
No full textOntology classification is the reasoning service that computes all subsumption relationships inferred in an ontology between concept, role, and attribute names in the ontology signature. OWL 2 QL is a tractable profile of OWL 2 for which ontology classification is polynomial in the size of the ontology TBox. However, to date, no efficient methods and implementations specifically tailored to OWL 2 QL ontologies have been developed. In this paper, we provide a new algorithm for ontology classification in OWL 2 QL, which is based on the idea of encoding the ontology TBox into a directed graph and reducing core reasoning to computation of the transitive closure of the graph. We have implemented the algorithm in the QuOnto reasoner and extensively evaluated it over very large ontologies. Our experiments show that QuOnto outperforms various popular reasoners in classification of OWL 2 QL ontologies. © 2013 Springer-Verlag Berlin Heidelberg
Efficient approximation in DL-Lite of OWL 2 ontologies
No full textOntologies, as a conceptualization of a domain of interest, can be used for different objectives, such as for providing a formal description of the domain of interest for documentation purposes, or for providing a mechanism for reasoning upon the domain. For instance, they are the core element of the Ontology-Based Data Access paradigm, in which the ontology is utilized as a conceptual view, allowing user access to the underlying data sources. With the aim to use an ontology as a formal description of the domain of interest, the use of expressive languages proves to be useful. If instead the goal is to use the ontology for reasoning tasks which require low computational complexity, the high expressivity of the language used to model the ontology may be of hindrance. In this scenario, the approximation of ontologies expressed in very expressive languages through ontologies expressed in languages which keep the computational complexity of the reasoning tasks low is pivotal. In this work we present our notion of ontology approximation and present an algorithm for computing the approximation of OWL 2 ontologies by means of DL-Lite TBoxes. Moreover, we provide optimization techniques for this computation, and discuss the results of the implementation of these techniques
A graph-based approach for classifying OWL 2 QL ontologies
No full textOntology classification is the reasoning service that computes all subsumption relationships inferred in an ontology between concept, role, and attribute names in the ontology signature. OWL 2 QL is a tractable profile of OWL 2 for which ontology classification is polynomial in the size of the ontology TBox. However, to date, no efficient methods and implementations specifically tailored to OWL 2 QL ontologies have been developed. In this paper, we provide a new algorithm for ontology classication in OWL 2 QL, which is based on the idea of encoding the ontology TBox into a directed graph and reducing core reasoning to computation of the transitive closure of the graph. We have implemented the algorithm in the QuOnto reasoner and extensively evaluated it over very large ontologies. Our experiments show that QuOnto outperforms various popular reasoners in classification of OWL 2 QL ontologies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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