88 research outputs found

    Flux de l'information en programmation logique

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    Cette thĂšse est dĂ©veloppĂ©e dans le but d'aborder la question du flux de l'information en programmation logique. Les contributions de cette thĂšse peuvent ĂȘtre divisĂ©es en trois parties: 1. Flux de l'information en programmation logique: Nous proposons une base thĂ©orique de ce que pourrait ĂȘtre un flux de l'information en programmation logique. Plusieurs dĂ©finitions de flux d'information (basĂ©es sur la rĂ©ussite / Ă©chec, les substitutions rĂ©ponses, bisimulation entre les arbres de rĂ©solution des buts logiques) sont Ă©valuĂ©es et comparĂ©es. Des problĂšmes de dĂ©cision sont donnĂ©s pour chaque dĂ©finition et la complexitĂ© est Ă©tudiĂ©e pour certaines catĂ©gories de programmes logiques. 2. Bisimulation de buts logiques: Nous introduisons la notion de bisimulation entre les buts Datalog: deux buts Datalog sont bisimilaires par rapport Ă  un programme Datalog donnĂ© lorsque leurs SLD-arbres, considĂ©rĂ©s comme des structures relationnelles, sont bisimilaires. Nous abordons le problĂšme de dĂ©cider si deux buts donnĂ©s sont bisimilaires Ă  l'Ă©gard d'un programme donnĂ©. Lorsque les programmes sont hiĂ©rarchiques ou restricted, ce problĂšme est dĂ©cidable en 2EXPTIME. 3. ContrĂŽle prĂ©ventif de l'infĂ©rence dans les bases de donnĂ©es dĂ©ductives: Nous proposons un mĂ©canisme de sĂ©curitĂ© sĂ»r et prĂ©cis pour les bases de donnĂ©es dĂ©ductives basĂ© sur la notion de flux de l'information dans la programmation logique.This thesis is developed in order to tackle the issue of information flow in logic programming. The contributions of this thesis can be split into three mains parts: 1. Information flow in logic programming: we propose a theoretical foundation of what could be an information flow in logic programming. Several information flow definitions (based on success/failure, substitution answers, bisimulation between resolution trees of goals) are stated and compared. Decision procedures are given for each definition and complexity is studied for specific classes of logic programs. 2. Bisimulation of logic goals: We introduce the concept of bisimulation between Datalog goals: two Datalog goals are bisimilar with respect to a given Datalog program when their SLD-trees, considered as relational structures, are bisimilar. We address the problem of deciding whether two given goals are bisimilar with respect to given programs. When the given programs are hierarchical or restricted, this problem is decidable in 2EXPTIME. 3. Preventive inference control for deductive databases: We propose a secure and a precise security mechanism for deductive databases based on the notion of information flow in logic programming

    Temporal Data Modeling and Reasoning for Information Systems

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    Temporal knowledge representation and reasoning is a major research field in Artificial Intelligence, in Database Systems, and in Web and Semantic Web research. The ability to model and process time and calendar data is essential for many applications like appointment scheduling, planning, Web services, temporal and active database systems, adaptive Web applications, and mobile computing applications. This article aims at three complementary goals. First, to provide with a general background in temporal data modeling and reasoning approaches. Second, to serve as an orientation guide for further specific reading. Third, to point to new application fields and research perspectives on temporal knowledge representation and reasoning in the Web and Semantic Web

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

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    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 tĂąche essentielle dans l’optimisation des requĂȘtes et la vĂ©rification de la base de graphes RDF. Nous Ă©tudions des techniques d’analyse statique pour SPARQL, le langage standard pour l’interrogation des donnĂ©es du Web sĂ©mantique. Plus prĂ©cisĂ©ment, nous Ă©tudions le problĂšme d’inclusion des requĂȘtes et de l’analyse de l’indĂ©pendance entre les requĂȘtes et la mise Ă  jour de la base de graphes RDF.Nous sommes intĂ©ressĂ©s par le dĂ©veloppement de techniques grĂące Ă  des rĂ©ductions au problĂšme de la satisfaisabilitĂ© de la logique.Nous nous traitons le problĂšme d’inclusion des requĂȘtes SPARQL en prĂ©sence de l’opĂ©rateur OPTIONAL. L’optionalitĂ© est l’un des constructeurs les plus compliquĂ©s dans SPARQL et aussi celui qui rend ce langage plus expressif que les langages de requĂȘtes classiques, comme SQL.Nous nous concentrons sur la classe de requĂȘtes appelĂ©e "well-designed SPARQL", proposĂ©es dans la littĂ©rature comme un fragment du langage avec de bonnes propriĂ©tĂ©s en matiĂšre d’évaluation des requĂȘtes incluent l’opĂ©ration OPTIONAL. À ce jour, l’inclusion de requĂȘte a Ă©tĂ© testĂ©e Ă  l’aide de diffĂ©rentes techniques: homomorphisme de graphes, bases de donnĂ©es canoniques, techniques de la thĂ©orie des automates et rĂ©duction au problĂšme de la validitĂ© d’une logique. Dans cette thĂšse, nous utilisons la derniĂšre technique pour tester l’inclusion des requĂȘtes SPARQL avec OPTIONAL utilisant une logique expressive appelĂ©e «logique K». En utilisant cette technique, il est possible de rĂ©gler le problĂšme d’inclusion des requĂȘtes pour plusieurs fragment de SPARQL, mĂȘme en prĂ©sence de schĂ©mas. Cette extensibilitĂ© n’est pas garantie par les autres mĂ©thodes.Nous montrons comment traduire a graphe RDF en un systĂšme de transitions, ainsi que une requĂȘte SPARQL en une formula K. Avec ces traductions, l’inclusion des requĂȘtes dans SPARQL peut ĂȘtre rĂ©duite au test de la validitĂ© d’une formule logique. Un avantage de cette approche est d’ouvrir la voie pour des implĂ©mentations utilisant solveurs de satisfiabilitĂ© pour K.Nous prĂ©sentons un banc d’essais de tests d’inclusion pour les requĂȘtes SPARQL avec OPTIONAL. Nous avons effectuĂ© des expĂ©riences pour tester et comparer des solveurs d’inclusion de l’état de l’art.Nous prĂ©sentons Ă©galement un aperçu prĂ©liminaire du problĂšme d’indĂ©pendance entre requĂȘte et mise Ă  jour. Une requĂȘte est indĂ©pendante de la mise Ă  jour lorsque l’exĂ©cution de la mise Ă  jour ne modifie pas le rĂ©sultat de la requĂȘte. Bien que ce problĂšme ait Ă©tĂ© intensivement Ă©tudiĂ© pour des fragments de calcul relationnel, il n’existe pas de travaux pour le langage de requĂȘtes standard pour le web sĂ©mantique. Nous proposons une dĂ©finition de la notion de l’indĂ©pendance dans le contexte de SPARQL et nous Ă©tablissons des premiĂšres pistes de analyse statique dans certains situations d’inclusion entre une requĂȘte et une mise Ă  jour

    Query-Based Multicontexts for Knowledge Base Browsing

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    Tirer parti de la structure des données incertaines

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    The management of data uncertainty can lead to intractability, in the case of probabilistic databases, or even undecidability, in the case of open-world reasoning under logical rules. My thesis studies how to mitigate these problems by restricting the structure of uncertain data and rules. My first contribution investigates conditions on probabilistic relational instances that ensure the tractability of query evaluation and lineage computation. I show that these tasks are tractable when we bound the treewidth of instances, for various probabilistic frameworks and provenance representations. Conversely, I show intractability under mild assumptions for any other condition on instances. The second contribution concerns query evaluation on incomplete data under logical rules, and under the finiteness assumption usually made in database theory. I show that this task is decidable for unary inclusion dependencies and functional dependencies. This establishes the first positive result for finite open-world query answering on an arbitrary-arity language featuring both referential constraints and number restrictions.La gestion des donnĂ©es incertaines peut devenir infaisable, dans le cas des bases de donnĂ©es probabilistes, ou mĂȘme indĂ©cidable, dans le cas du raisonnement en monde ouvert sous des contraintes logiques. Cette thĂšse Ă©tudie comment pallier ces problĂšmes en limitant la structure des donnĂ©es incertaines et des rĂšgles. La premiĂšre contribution prĂ©sentĂ©e s'intĂ©resse aux conditions qui permettent d'assurer la faisabilitĂ© de l'Ă©valuation de requĂȘtes et du calcul de lignage sur les instances relationnelles probabilistes. Nous montrons que ces tĂąches sont faisables, pour diverses reprĂ©sentations de la provenance et des probabilitĂ©s, quand la largeur d'arbre des instances est bornĂ©e. RĂ©ciproquement, sous des hypothĂšses faibles, nous pouvons montrer leur infaisabilitĂ© pour toute autre condition imposĂ©e sur les instances. La seconde contribution concerne l'Ă©valuation de requĂȘtes sur des donnĂ©es incomplĂštes et sous des contraintes logiques, sous l'hypothĂšse de finitude gĂ©nĂ©ralement supposĂ©e en thĂ©orie des bases de donnĂ©es. Nous montrons la dĂ©cidabilitĂ© de cette tĂąche pour les dĂ©pendances d'inclusion unaires et les dĂ©pendances fonctionnelles. Ceci constitue le premier rĂ©sultat positif, sous l'hypothĂšse de la finitude, pour la rĂ©ponse aux requĂȘtes en monde ouvert avec un langage d'aritĂ© arbitraire qui propose Ă  la fois des contraintes d'intĂ©gritĂ© rĂ©fĂ©rentielle et des contraintes de cardinalitĂ©

    COLAB : a hybrid knowledge representation and compilation laboratory

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    Knowledge bases for real-world domains such as mechanical engineering require expressive and efficient representation and processing tools. We pursue a declarative-compilative approach to knowledge engineering. While Horn logic (as implemented in PROLOG) is well-suited for representing relational clauses, other kinds of declarative knowledge call for hybrid extensions: functional dependencies and higher-order knowledge should be modeled directly. Forward (bottom-up) reasoning should be integrated with backward (top-down) reasoning. Constraint propagation should be used wherever possible instead of search-intensive resolution. Taxonomic knowledge should be classified into an intuitive subsumption hierarchy. Our LISP-based tools provide direct translators of these declarative representations into abstract machines such as an extended Warren Abstract Machine (WAM) and specialized inference engines that are interfaced to each other. More importantly, we provide source-to-source transformers between various knowledge types, both for user convenience and machine efficiency. These formalisms with their translators and transformers have been developed as part of COLAB, a compilation laboratory for studying what we call, respectively, "vertical\u27; and "horizontal\u27; compilation of knowledge, as well as for exploring the synergetic collaboration of the knowledge representation formalisms. A case study in the realm of mechanical engineering has been an important driving force behind the development of COLAB. It will be used as the source of examples throughout the paper when discussing the enhanced formalisms, the hybrid representation architecture, and the compilers

    International Workshop on Description Logics : Bonn, May 28/29, 1994

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    This collection of papers forms the permanent record of the 1994 Description Logic Workshop, that was held at the Gustav Stresemann Institut in Bonn, Germany on 28 and 29 May 1994, immediately after the Fourth International Conference on Principles of Knowledge Representation and Reasoning. The workshop was set up to be as informal as possible, so this collection cannot hope to capture the discussions associated with the workshop. However, we hope that it will serve to remind participants of their discussion at the workshop, and provide non-participants with indications of the topics that were discussed at the workshop. The workshop consisted of seven regular sessions and one panel session. Each regular session had about four short presentations on a single theme, but also had considerable time reserved for discussion. The themes of the sessions were Foundations of Description Logics, Architecture of Description Logics and Description Logic Systems, Language Extensions, Expanding Description Logics, General Applications of Description Logics, Natural Language Applications of Description Logics, Connections between Description Logics and Databases, and the Future of Description Logics and Description Logic Systems. The session on Foundations of Description Logics concentrated on computational properties of description logics, correspondences between description logics and other formalisms, and on semantics of description logics, Similarly, there is discussion on how to develop tractable desription logics, for some notion of tractable, and whether it is useful to worry about achieving tractability at all. Several of the participants argued in favour of a very expressive description logic. This obviously precludes tractability or even decidability of complete reasoning. Klaus Schild proposed that for some purposes one could employ "model checking" (i .e., a closed world assumption) instead of "theorem proving," and has shown that this is still tractable for very large languages. Maurizio Lenzerini's opinion was that it is important to have decidable languages. Tractability cannot be achieved in several application areas because there one needs very expressive constructs: e.g., axioms, complex role constructors, and cycles with fixed-point semantics. For Bob MacGregor, not even decidability is an issue since he claims that Loom's incomplete reasoner is sufficient for his applications. The discussion addressed the question of whether there is still need for foundations, and whether the work on foundation done until now really solved the problems that the designers of early DL systems had. Both questions were mostly answered in the affirmative, with the caveat that new research on foundations should make sure that it is concerned with "real" problems, and not just generates new problems. In the session on Architecture of Description Logics and Description Logic Systems the participants considered different ways of putting together description logics and description logic systems. One way of doing this is to have a different kind of inference strategy for description logics, such as one based on intuitionistic logics or one based directly on rules of inference-thus allowing variant systems. Another way of modifying description logic systems is to divide them up in different ways, such as making a terminology consist of a schema portion and a view portion. Some discussion in this session concerned whether architectures should be influenced by application areas, or even by particular applications. There was considerable discussion at the workshop on how Description Logics should be extended or expanded to make them more useful. There are several methods to do this. The first is to extend the language of descriptions, e.g ., to represent n-ary relations, temporal information, or whole-part relationships, all of which were discussed at the workshop. The second is to add in another kind of reasoning, such as default reasoning, while still keeping the general framework of description logic reasoning. The third is to incorporate descriptions or description-like constructs in a larger reasoner, such as a first order reasoner. This was the approach taken in OMEGA and is the approach being taken in the Loom project. There have been many extensions of the first two kinds proposed for description logics, including several presented at the workshop. One quest ion discussed at the workshop was whether these extensions fit in well with the philosophy of description logic. Another question was whether the presence of many proposals for extensions means that description logics are easy to expand, or that description logics are inadequate representation formalisms? The general consensus was that description logics adequately capture a certain kind of core reasoning and that they lend themselves to incorporation with other kinds of reasoning. Care must be taken, however, to keep the extended versions true to the goals of description logics. The sessions on Applications of Description Logics had presentations on applications of description logics in various areas, including configuration, tutoring, natural language processing, and domain modeling. Most of these applications are research applications, funded by government research programs. There was discussion of what is needed to have more fielded applications of description logics. The session on Connections between Description Logics and Databases considered three kinds of connections between Description Logics and Databases: 1. using Description Logics for expressing database schemas, including local schemas, integrated schemas, and views, integrity constraints, and queries; 2. using Description Logic reasoning for various database-related reasoning, including schema integration and validation, and query optimization, and query validation and organization; and 3. making Description Logic reasoners more like Database Mangagement Systems via optimization. All three of these connections are being actively investigated by the description logic community. The panel session on the Future of Description Logics and Description Logic Systems discussed where the future of description logics will lie. There seems to be a consensus that description logics must forge tighter connections with other formalisms, such as databases or object-oriented systems. In this way, perhaps, description logics will find more real applications

    International Workshop on Description Logics : Bonn, May 28/29, 1994

    Get PDF
    This collection of papers forms the permanent record of the 1994 Description Logic Workshop, that was held at the Gustav Stresemann Institut in Bonn, Germany on 28 and 29 May 1994, immediately after the Fourth International Conference on Principles of Knowledge Representation and Reasoning. The workshop was set up to be as informal as possible, so this collection cannot hope to capture the discussions associated with the workshop. However, we hope that it will serve to remind participants of their discussion at the workshop, and provide non-participants with indications of the topics that were discussed at the workshop. The workshop consisted of seven regular sessions and one panel session. Each regular session had about four short presentations on a single theme, but also had considerable time reserved for discussion. The themes of the sessions were Foundations of Description Logics, Architecture of Description Logics and Description Logic Systems, Language Extensions, Expanding Description Logics, General Applications of Description Logics, Natural Language Applications of Description Logics, Connections between Description Logics and Databases, and the Future of Description Logics and Description Logic Systems. The session on Foundations of Description Logics concentrated on computational properties of description logics, correspondences between description logics and other formalisms, and on semantics of description logics, Similarly, there is discussion on how to develop tractable desription logics, for some notion of tractable, and whether it is useful to worry about achieving tractability at all. Several of the participants argued in favour of a very expressive description logic. This obviously precludes tractability or even decidability of complete reasoning. Klaus Schild proposed that for some purposes one could employ "model checking" (i .e., a closed world assumption) instead of "theorem proving," and has shown that this is still tractable for very large languages. Maurizio Lenzerini's opinion was that it is important to have decidable languages. Tractability cannot be achieved in several application areas because there one needs very expressive constructs: e.g., axioms, complex role constructors, and cycles with fixed-point semantics. For Bob MacGregor, not even decidability is an issue since he claims that Loom's incomplete reasoner is sufficient for his applications. The discussion addressed the question of whether there is still need for foundations, and whether the work on foundation done until now really solved the problems that the designers of early DL systems had. Both questions were mostly answered in the affirmative, with the caveat that new research on foundations should make sure that it is concerned with "real" problems, and not just generates new problems. In the session on Architecture of Description Logics and Description Logic Systems the participants considered different ways of putting together description logics and description logic systems. One way of doing this is to have a different kind of inference strategy for description logics, such as one based on intuitionistic logics or one based directly on rules of inference-thus allowing variant systems. Another way of modifying description logic systems is to divide them up in different ways, such as making a terminology consist of a schema portion and a view portion. Some discussion in this session concerned whether architectures should be influenced by application areas, or even by particular applications. There was considerable discussion at the workshop on how Description Logics should be extended or expanded to make them more useful. There are several methods to do this. The first is to extend the language of descriptions, e.g ., to represent n-ary relations, temporal information, or whole-part relationships, all of which were discussed at the workshop. The second is to add in another kind of reasoning, such as default reasoning, while still keeping the general framework of description logic reasoning. The third is to incorporate descriptions or description-like constructs in a larger reasoner, such as a first order reasoner. This was the approach taken in OMEGA and is the approach being taken in the Loom project. There have been many extensions of the first two kinds proposed for description logics, including several presented at the workshop. One quest ion discussed at the workshop was whether these extensions fit in well with the philosophy of description logic. Another question was whether the presence of many proposals for extensions means that description logics are easy to expand, or that description logics are inadequate representation formalisms? The general consensus was that description logics adequately capture a certain kind of core reasoning and that they lend themselves to incorporation with other kinds of reasoning. Care must be taken, however, to keep the extended versions true to the goals of description logics. The sessions on Applications of Description Logics had presentations on applications of description logics in various areas, including configuration, tutoring, natural language processing, and domain modeling. Most of these applications are research applications, funded by government research programs. There was discussion of what is needed to have more fielded applications of description logics. The session on Connections between Description Logics and Databases considered three kinds of connections between Description Logics and Databases: 1. using Description Logics for expressing database schemas, including local schemas, integrated schemas, and views, integrity constraints, and queries; 2. using Description Logic reasoning for various database-related reasoning, including schema integration and validation, and query optimization, and query validation and organization; and 3. making Description Logic reasoners more like Database Mangagement Systems via optimization. All three of these connections are being actively investigated by the description logic community. The panel session on the Future of Description Logics and Description Logic Systems discussed where the future of description logics will lie. There seems to be a consensus that description logics must forge tighter connections with other formalisms, such as databases or object-oriented systems. In this way, perhaps, description logics will find more real applications
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