Query inseparability for ALC ontologies

We investigate the problem whether two ALC ontologies are indistinguishable (or inseparable) by means of queries in a given signature, which is fundamental for ontology engineering tasks such as ontology versioning, modularisation, update, and forgetting. We consider both knowledge base (KB) and TBox inseparability. For KBs, we give model-theoretic criteria in terms of (finite partial) homomorphisms and products and prove that this problem is undecidable for conjunctive queries (CQs), but 2ExpTime-complete for unions of CQs (UCQs). The same results hold if (U)CQs are replaced by rooted (U)CQs, where every variable is connected to an answer variable. We also show that inseparability by CQs is still undecidable if one KB is given in the lightweight DL EL and if no restrictions are imposed on the signature of the CQs. We also consider the problem whether two ALC TBoxes give the same answers to any query over any ABox in a given signature and show that, for CQs, this problem is undecidable, too. We then develop model-theoretic criteria for HornALC TBoxes and show using tree automata that, in contrast, inseparability becomes decidable and 2ExpTime-complete, even ExpTime-complete when restricted to (unions of) rooted CQs

Reasoning & Querying – State of the Art

Various query languages for Web and Semantic Web data, both for practical use and as an area of research in the scientific community, have emerged in recent years. At the same time, the broad adoption of the internet where keyword search is used in many applications, e.g. search engines, has familiarized casual users with using keyword queries to retrieve information on the internet. Unlike this easy-to-use querying, traditional query languages require knowledge of the language itself as well as of the data to be queried. Keyword-based query languages for XML and RDF bridge the gap between the two, aiming at enabling simple querying of semi-structured data, which is relevant e.g. in the context of the emerging Semantic Web. This article presents an overview of the field of keyword querying for XML and RDF

Containment for Rule-Based Ontology-Mediated Queries

Many efforts have been dedicated to identifying restrictions on ontologies expressed as tuple-generating dependencies (tgds), a.k.a. existential rules, that lead to the decidability for the problem of answering ontology-mediated queries (OMQs). This has given rise to three families of formalisms: guarded, non-recursive, and sticky sets of tgds. In this work, we study the containment problem for OMQs expressed in such formalisms, which is a key ingredient for solving static analysis tasks associated with them. Our main contribution is the development of specially tailored techniques for OMQ containment under the classes of tgds stated above. This enables us to obtain sharp complexity bounds for the problems at hand, which in turn allow us to delimitate its practical applicability. We also apply our techniques to pinpoint the complexity of problems associated with two emerging applications of OMQ containment: distribution over components and UCQ rewritability of OMQs

Web and Semantic Web Query Languages

A number of techniques have been developed to facilitate powerful data retrieval on the Web and Semantic Web. Three categories of Web query languages can be distinguished, according to the format of the data they can retrieve: XML, RDF and Topic Maps. This article introduces the spectrum of languages falling into these categories and summarises their salient aspects. The languages are introduced using common sample data and query types. Key aspects of the query languages considered are stressed in a conclusion

Sur l'analyse statique des requêtes SPARQL avec la logique modale

Static analysis is a core task in query optimization and knowledge base verification. We study static analysis techniques for SPARQL, the standard language for querying Semantic Web data. Specifically, we investigate the query containment problem and the query-update independence analysis. We are interested in developing techniques through reductions to the validity problem in logic.We address SPARQL query containment with optional matching. We focus on the class of well-designed SPARQL queries, proposed in the literature as a fragment of the language with good properties regarding query evaluation. SPARQL is interpreted over graphs, hence we encode it in a graph logic, specifically the modal logic K interpreted over label transition systems. We show that this logic is powerful enough to deal with query containment for the well-designed fragment of SPARQL. We show how to translate RDF graphs into transition systems and SPARQL queries into K-formulae. Therefore, query containment in SPARQL can be reduced to unsatisfiability in K.We also report on a preliminary overview of the SPARQL query-update problem. A query is independent of an update when the execution of the update does not affect the result of the query. Determining independence is especially useful in the contest of huge RDF repositories, where it permits to avoid expensive yet useless re-evaluation of queries. While this problem has been intensively studied for fragments of relational calculus, no works exist for the standard query language for the semantic web. We report on our investigations on how a notion of independence can be defined in the SPARQL contextL’analyse statique est une tâche essentielle dans l’optimisation des requêtes et la vérification de la base de graphes RDF. Nous étudions des techniques d’analyse statique pour SPARQL, le langage standard pour l’interrogation des données du Web sémantique. Plus précisément, nous étudions le problème d’inclusion des requêtes et de l’analyse de l’indépendance entre les requêtes et la mise à jour de la base de graphes RDF.Nous sommes intéressés par le développement de techniques grâce à des réductions au problème de la satisfaisabilité de la logique.Nous nous traitons le problème d’inclusion des requêtes SPARQL en présence de l’opérateur OPTIONAL. L’optionalité est l’un des constructeurs les plus compliqués dans SPARQL et aussi celui qui rend ce langage plus expressif que les langages de requêtes classiques, comme SQL.Nous nous concentrons sur la classe de requêtes appelée "well-designed SPARQL", proposées dans la littérature comme un fragment du langage avec de bonnes propriétés en matière d’évaluation des requêtes incluent l’opération OPTIONAL. À ce jour, l’inclusion de requête a été testée à l’aide de différentes techniques: homomorphisme de graphes, bases de données canoniques, techniques de la théorie des automates et réduction au problème de la validité d’une logique. Dans cette thèse, nous utilisons la dernière technique pour tester l’inclusion des requêtes SPARQL avec OPTIONAL utilisant une logique expressive appelée «logique K». En utilisant cette technique, il est possible de régler le problème d’inclusion des requêtes pour plusieurs fragment de SPARQL, même en présence de schémas. Cette extensibilité n’est pas garantie par les autres méthodes.Nous montrons comment traduire a graphe RDF en un système de transitions, ainsi que une requête SPARQL en une formula K. Avec ces traductions, l’inclusion des requêtes dans SPARQL peut être réduite au test de la validité d’une formule logique. Un avantage de cette approche est d’ouvrir la voie pour des implémentations utilisant solveurs de satisfiabilité pour K.Nous présentons un banc d’essais de tests d’inclusion pour les requêtes SPARQL avec OPTIONAL. Nous avons effectué des expériences pour tester et comparer des solveurs d’inclusion de l’état de l’art.Nous présentons également un aperçu préliminaire du problème d’indépendance entre requête et mise à jour. Une requête est indépendante de la mise à jour lorsque l’exécution de la mise à jour ne modifie pas le résultat de la requête. Bien que ce problème ait été intensivement étudié pour des fragments de calcul relationnel, il n’existe pas de travaux pour le langage de requêtes standard pour le web sémantique. Nous proposons une définition de la notion de l’indépendance dans le contexte de SPARQL et nous établissons des premières pistes de analyse statique dans certains situations d’inclusion entre une requête et une mise à jour

O balanceamento contra a China com o corredor de crescimento Ásia-África: uma iniciativa indiana-japonesa para o Indo-Pacífico

This paper aims to analyse whether the Indian-Japanese initiative Asia-Africa Growth Corridor (AAGC) can be considered a strategy to curb China's supposed capacity of diplomatically isolating its regional rivals while attempting to consolidate the Indo-Pacific as an area of influence. The hypothesis is that, in a moment of uncertainty over United States’ commitment with their Asian traditional partners and allies, India and Japan are encouraged to develop new mechanisms to balance against China. According to the Realist school of International Relations, India and Japan will virtually seek manners to balance against China in order to defend their interests. This paper develops the argument using the concepts of ‘balancing of threat’ and ‘soft balancing’ to describe the strategies developed by these countries within the Indo-Pacific.Este artigo pretende analisar se a iniciativa Indiana-Japonesa do Corredor de Crescimento Ásia-África (AAGC) pode ser considerada uma estratégia para conter a suposta capacidade da China de isolar diplomaticamente seus rivais regionais, enquanto tenta consolidar o Indo-Pacífico como uma área de influência. A hipótese é que, em um momento de incerteza sobre o compromisso dos Estados Unidos com seus parceiros tradicionais asiáticos e aliados, a Índia e o Japão são encorajados a desenvolver novos mecanismos para equilibrar a China. Segundo a escola realista de Relações Internacionais, a Índia e o Japão buscarão virtualmente maneiras de equilibrar-se contra a China a fim de defender seus interesses. Este artigo desenvolve o argumento usando os conceitos de "equilíbrio da ameaça" e "balanceamento suave" para descrever as estratégias desenvolvidas por esses países dentro do Indo-Pacífico

When is Ontology-Mediated Querying Efficient?

In ontology-mediated querying, description logic (DL) ontologies are used to enrich incomplete data with domain knowledge which results in more complete answers to queries. However, the evaluation of ontology-mediated queries (OMQs) over relational databases is computationally hard. This raises the question when OMQ evaluation is efficient, in the sense of being tractable in combined complexity or fixed-parameter tractable. We study this question for a range of ontology-mediated query languages based on several important and widely-used DLs, using unions of conjunctive queries as the actual queries. For the DL ELHI extended with the bottom concept, we provide a characterization of the classes of OMQs that are fixed-parameter tractable. For its fragment EL extended with domain and range restrictions and the bottom concept (which restricts the use of inverse roles), we provide a characterization of the classes of OMQs that are tractable in combined complexity. Both results are in terms of equivalence to OMQs of bounded tree width and rest on a reasonable assumption from parameterized complexity theory. They are similar in spirit to Grohe's seminal characterization of the tractable classes of conjunctive queries over relational databases. We further study the complexity of the meta problem of deciding whether a given OMQ is equivalent to an OMQ of bounded tree width, providing several completeness results that range from NP to 2ExpTime, depending on the DL used. We also consider the DL-Lite family of DLs, including members that admit functional roles

An Ontology-Driven Sociomedical Web 3.0 Framework

Web 3.0, the web of social and semantic cooperation, calls for a methodological multidisciplinary architecture in order to reach its mainstream objectives. With the lack of such an architecture and the reliance of existing efforts on lightweight semantics and RDF graphs, this thesis proposes "Web3.OWL", an ontology-driven framework towards a Web 3.0 knowledge architecture. Meanwhile, the online social parenting data and their corresponding websites users known as "mommy bloggers" undergo one of the fastest online demographics growth, and the available literature reflects the very little attention this growth has so far been given and the various deficiencies the parenting domain suffers from; these deficiencies all fall under the umbrella of the scarcity of parenting sociomedical analysis and decision-support systems. The Web3.OWL framework puts forward an approach that relies on the Meta-Object Facility for Semantics standard (SMOF) for the management of its modeled OWL (Web Ontology Language) expressive domain ontologies on the one hand, and the coordination of its various underlined Web 3.0 prerequisite disciplines on the other. Setting off with a holistic portrayal of Web3.OWL’s components and workflow, the thesis progresses into a more analytic exploration of its main paradigms. Out of its different ontology-aware paradigms are notably highlighted both its methodology for expressiveness handling through modularization and projection techniques and algorithms, and its facilities for tagging inference, suggestion and processing. Web3.OWL, albeit generic by conception, proves its efficiency in solving the deficiencies and meeting the requirements of the sociomedical domain of interest. Its conceived ontology for parenting analysis and surveillance, baptised "ParOnt", strongly contributes to the backbone metamodel and the various constituents of this ontology-driven framework. Accordingly, as the workflow revolves around Description Logics principles, OWL 2 profiles along with standard and beyond-standard reasoning techniques, conducted experiments and competency questions are illustrated, thus establishing the required Web 3.0 outcomes. The empirical results of the diverse preliminary decision-support and recommendation services targeting parenting public awareness, orientation and education do ascertain, in conclusion, the value and potentials of the proposed conceptual framework