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Werner Nutt - One of the best experts on this subject based on the ideXlab platform.

  • International Semantic Web Conference (Posters & Demos) - Bridging the semantic gap between RDF and SPARQL using completeness statements
    2014
    Co-Authors: Fariz Darari, Simon Razniewski, Werner Nutt
    Abstract:

    RDF data is often treated as incomplete, following the Open-World Assumption. On the other hand, SPARQL, the standard query language over RDF, usually follows the Closed-World Assumption, assuming RDF data to be complete. This gives rise to a semantic gap between RDF and SPARQL. In this paper, we address how to close the semantic gap between RDF and SPARQL in terms of certain answers and possible answers using completeness statements.

  • Bridging the Semantic Gap between RDF and SPARQL using Completeness Statements [Extended Version].
    arXiv: Databases, 2014
    Co-Authors: Fariz Darari, Simon Razniewski, Werner Nutt
    Abstract:

    RDF data is often treated as incomplete, following the Open-World Assumption. On the other hand, SPARQL, the standard query language over RDF, usually follows the Closed-World Assumption, assuming RDF data to be complete. This gives rise to a semantic gap between RDF and SPARQL. In this paper, we address how to close the semantic gap between RDF and SPARQL in terms of certain answers and possible answers using completeness statements.

  • databases under the partial Closed World Assumption a survey
    Grundlagen von Datenbanken, 2014
    Co-Authors: Simon Razniewski, Werner Nutt
    Abstract:

    Databases are traditionally considered either under the ClosedWorld or the open-World Assumption. In some scenarios however a middle ground, the partial Closed-World Assumption, is needed, which has received less attention so far. In this survey we review foundational and work on the partial Closed-World Assumption and then discuss work done in our group in recent years on various aspects of reasoning over databases under this Assumption. We first discuss the conceptual foundations of this Assumption. We then list the main decision problems and the known results. Finally, we discuss implementational approaches and extensions.

  • Grundlagen von Datenbanken - Databases under the Partial Closed-World Assumption: A Survey.
    2014
    Co-Authors: Simon Razniewski, Werner Nutt
    Abstract:

    Databases are traditionally considered either under the ClosedWorld or the open-World Assumption. In some scenarios however a middle ground, the partial Closed-World Assumption, is needed, which has received less attention so far. In this survey we review foundational and work on the partial Closed-World Assumption and then discuss work done in our group in recent years on various aspects of reasoning over databases under this Assumption. We first discuss the conceptual foundations of this Assumption. We then list the main decision problems and the known results. Finally, we discuss implementational approaches and extensions.

Simon Razniewski - One of the best experts on this subject based on the ideXlab platform.

  • International Semantic Web Conference (Posters & Demos) - Bridging the semantic gap between RDF and SPARQL using completeness statements
    2014
    Co-Authors: Fariz Darari, Simon Razniewski, Werner Nutt
    Abstract:

    RDF data is often treated as incomplete, following the Open-World Assumption. On the other hand, SPARQL, the standard query language over RDF, usually follows the Closed-World Assumption, assuming RDF data to be complete. This gives rise to a semantic gap between RDF and SPARQL. In this paper, we address how to close the semantic gap between RDF and SPARQL in terms of certain answers and possible answers using completeness statements.

  • Bridging the Semantic Gap between RDF and SPARQL using Completeness Statements [Extended Version].
    arXiv: Databases, 2014
    Co-Authors: Fariz Darari, Simon Razniewski, Werner Nutt
    Abstract:

    RDF data is often treated as incomplete, following the Open-World Assumption. On the other hand, SPARQL, the standard query language over RDF, usually follows the Closed-World Assumption, assuming RDF data to be complete. This gives rise to a semantic gap between RDF and SPARQL. In this paper, we address how to close the semantic gap between RDF and SPARQL in terms of certain answers and possible answers using completeness statements.

  • databases under the partial Closed World Assumption a survey
    Grundlagen von Datenbanken, 2014
    Co-Authors: Simon Razniewski, Werner Nutt
    Abstract:

    Databases are traditionally considered either under the ClosedWorld or the open-World Assumption. In some scenarios however a middle ground, the partial Closed-World Assumption, is needed, which has received less attention so far. In this survey we review foundational and work on the partial Closed-World Assumption and then discuss work done in our group in recent years on various aspects of reasoning over databases under this Assumption. We first discuss the conceptual foundations of this Assumption. We then list the main decision problems and the known results. Finally, we discuss implementational approaches and extensions.

  • Grundlagen von Datenbanken - Databases under the Partial Closed-World Assumption: A Survey.
    2014
    Co-Authors: Simon Razniewski, Werner Nutt
    Abstract:

    Databases are traditionally considered either under the ClosedWorld or the open-World Assumption. In some scenarios however a middle ground, the partial Closed-World Assumption, is needed, which has received less attention so far. In this survey we review foundational and work on the partial Closed-World Assumption and then discuss work done in our group in recent years on various aspects of reasoning over databases under this Assumption. We first discuss the conceptual foundations of this Assumption. We then list the main decision problems and the known results. Finally, we discuss implementational approaches and extensions.

Maurice Bruynooghe - One of the best experts on this subject based on the ideXlab platform.

  • KR - Accuracy and efficiency of fixpoint methods for approximate query answering in locally complete databases
    2008
    Co-Authors: Álvaro Cortés-calabuig, Marc Denecker, Ofer Arieli, Maurice Bruynooghe
    Abstract:

    Standard databases convey Reiter's Closed-World Assumption that an atom not in the database is false. This Assumption is relaxed in locally Closed databases that are sound but only partially complete about their domain. One of the consequences of the weakening of the Closed-World Assumption is that query answering in locally Closed databases is undecidable. In this paper, we develop efficient approximate methods for query answering, based on fixpoint computations, and investigate conditions that assure the optimality of these methods. Our approach of approximative reasoning may be incorporated in different contexts where incompleteness plays a major role and efficient reasoning is imperative.

  • AAAI - Approximate query answering in locally Closed databases
    2007
    Co-Authors: Álvaro Cortés-calabuig, Marc Denecker, Ofer Arieli, Maurice Bruynooghe
    Abstract:

    The Closed-World Assumption (CWA) on databases expresses that an atom not in the database is false. A more appropriate Assumption for databases that are sound but partially incomplete, is the Local Closed-World Assumption (LCWA), which is a local form of the CWA, expressing that the database is complete in a certain area, called the 'window of expertise'. Databases consisting of a standard database instance augmented with a collection of LCWA's are called locally Closed databases. In this paper, we investigate the complexity of certain and possible query answering in such databases. As it tums out that these problems are intractlble, we develop efficient approximate methods to underestimate certain answers and overestimate possible answers. We prove that under certain conditions, our methods produce complete answers.

  • LPAR - Representation of partial knowledge and query answering in locally complete databases
    Logic for Programming Artificial Intelligence and Reasoning, 2006
    Co-Authors: Álvaro Cortés-calabuig, Marc Denecker, Ofer Arieli, Maurice Bruynooghe
    Abstract:

    The Local Closed-World Assumption (LCWA) is a generalization of Reiter's Closed-World Assumption (CWA) for relational databases that may be incomplete. Two basic questions that are related to this Assumption are: (1) how to represent the fact that only part of the information is known to be complete, and (2) how to properly reason with this information, that is: how to determine whether an answer to a database query is complete even though the database information is incomplete. In this paper we concentrate on the second issue based on a treatment of the first issue developed in earlier work of the authors. For this we consider a fixpoint semantics for declarative theories that represent locally complete databases. This semantics is based on 3-valued interpretations that allow to distinguish between the certain and possible consequences of the database's theory.

  • on the local Closed World Assumption of data sources
    International Conference on Logic Programming, 2005
    Co-Authors: Alvaro Cortescalabuig, Marc Denecker, Ofer Arieli, Bert Van Nuffelen, Maurice Bruynooghe
    Abstract:

    The Closed-World Assumption (CWA) on a database expresses that an atom not in the database is false. The CWA is only applicable in domains where the database has complete knowledge. In many cases, for example in the context of distributed databases, a data source has only complete knowledge about part of the domain of discourse. In this paper, we introduce an expressive and intuitively appealing method of representing a local Closed-World Assumption (LCWA) of autonomous data-sources. This approach distinguishes between the data that is conveyed by a data-source and the meta-knowledge about the area in which these data is complete. The data is stored in a relational database that can be queried in the standard way, whereas the meta-knowledge about its completeness is expressed by a first order theory that can be processed by an independent reasoning system (for example a mediator). We consider different ways of representing our approach, relate it to other methods of representing local Closed-word Assumptions of data-sources, and show some useful properties of our framework which facilitate its application in real-life systems.

  • BNAIC - On the local Closed-World Assumption of data-sources
    Logic Programming and Nonmonotonic Reasoning, 2005
    Co-Authors: Álvaro Cortés-calabuig, Marc Denecker, Ofer Arieli, Bert Van Nuffelen, Maurice Bruynooghe
    Abstract:

    The Closed-World Assumption (CWA) on a database expresses that an atom not in the database is false. The CWA is only applicable in domains where the database has complete knowledge. In many cases, for example in the context of distributed databases, a data source has only complete knowledge about part of the domain of discourse. In this paper, we introduce an expressive and intuitively appealing method of representing a local Closed-World Assumption (LCWA) of autonomous data-sources. This approach distinguishes between the data that is conveyed by a data-source and the meta-knowledge about the area in which these data is complete. The data is stored in a relational database that can be queried in the standard way, whereas the meta-knowledge about its completeness is expressed by a first order theory that can be processed by an independent reasoning system (for example a mediator). We consider different ways of representing our approach, relate it to other methods of representing local Closed-word Assumptions of data-sources, and show some useful properties of our framework which facilitate its application in real-life systems.

Alain Leger - One of the best experts on this subject based on the ideXlab platform.

  • semantic web service composition based on a Closed World Assumption
    European Conference on Web Services, 2006
    Co-Authors: Freddy Lecue, Alain Leger
    Abstract:

    Automation of Web service composition i.e., the process of forming new value added Web services is one of the most promising challenges in Web service research area. Such an automation does not involve only a richer semantic for Web service description but also reasoning processes about those descriptions. Semantics is supposed to be one of the key elements for the automation of Web service composition. Indeed semantic Web services enable a rich machine-understandable descriptions of their capabilities and processes in order to ease automation of processes such as discovery, selection and composition. In this paper one studies the functional level description of Web services and its impact on Web service composition hence the presentation of a formal model CLM (causal link matrix). The model supports a semantic context in order to find a correct, complete and consistent plan as an AI planning-based composition. The innovative and formal model follows a forward chaining-oriented composition. Moreover two methods of optimization (i.e., local-oriented and a global-oriented) of Web service composition are introduced to discover the best plan according to a semantic criterion i.e., the causal link between Web services

  • ECOWS - Semantic Web Service Composition Based on a Closed World Assumption
    2006 European Conference on Web Services (ECOWS'06), 2006
    Co-Authors: Freddy Lecue, Alain Leger
    Abstract:

    Automation of Web service composition i.e., the process of forming new value added Web services is one of the most promising challenges in Web service research area. Such an automation does not involve only a richer semantic for Web service description but also reasoning processes about those descriptions. Semantics is supposed to be one of the key elements for the automation of Web service composition. Indeed semantic Web services enable a rich machine-understandable descriptions of their capabilities and processes in order to ease automation of processes such as discovery, selection and composition. In this paper one studies the functional level description of Web services and its impact on Web service composition hence the presentation of a formal model CLM (causal link matrix). The model supports a semantic context in order to find a correct, complete and consistent plan as an AI planning-based composition. The innovative and formal model follows a forward chaining-oriented composition. Moreover two methods of optimization (i.e., local-oriented and a global-oriented) of Web service composition are introduced to discover the best plan according to a semantic criterion i.e., the causal link between Web services

German Rigau - One of the best experts on this subject based on the ideXlab platform.

  • Applying the Closed World Assumption to SUMO-based Ontologies.
    arXiv: Artificial Intelligence, 2018
    Co-Authors: Javier Álvez, Itziar Gonzalez-dios, German Rigau
    Abstract:

    In commonsense knowledge representation, the Open World Assumption is adopted as a general standard strategy for the design, construction and use of ontologies, e.g. in OWL. This strategy limits the inferencing capabilities of any system using these ontologies because non-asserted statements could be assumed to be alternatively true or false in different interpretations. In this paper, we investigate the application of the Closed World Assumption to enable a better exploitation of the structural knowledge encoded in a SUMO-based ontology. To that end, we explore three different Closed World Assumption formulations for subclass and disjoint relations in order to reduce the ambiguity of the knowledge encoded in first-order logic ontologies. We evaluate these formulations on a practical experimentation using a very large commonsense benchmark automatically obtained from the knowledge encoded in WordNet through its mapping to SUMO. The results show that the competency of the ontology improves more than 47 % when reasoning under the Closed World Assumption. As conclusion, applying the Closed World Assumption automatically to first-order logic ontologies reduces their expressed ambiguity and more commonsense questions can be answered.

  • Applying the Closed World Assumption to SUMO-based FOL Ontologies for Effective Commonsense Reasoning
    arXiv: Artificial Intelligence, 2018
    Co-Authors: Javier Álvez, Itziar Gonzalez-dios, German Rigau
    Abstract:

    Most commonly, the Open World Assumption is adopted as a standard strategy for the design, construction and use of ontologies. This strategy limits the inferencing capabilities of any system because non-asserted statements (missing knowledge) could be assumed to be alternatively true or false. As we will demonstrate, this is especially the case of first-order logic (FOL) ontologies where non-asserted statements is nowadays one of the main obstacles to its practical application in automated commonsense reasoning tasks. In this paper, we investigate the application of the Closed World Assumption (CWA) to enable a better exploitation of FOL ontologies by using state-of-the-art automated theorem provers. To that end, we explore different CWA formulations for the structural knowledge encoded in a FOL translation of the SUMO ontology, discovering that almost 30 % of the structural knowledge is missing. We evaluate these formulations on a practical experimentation using a very large commonsense benchmark obtained from WordNet through its mapping to SUMO. The results show that the competency of the ontology improves more than 50 % when reasoning under the CWA. Thus, applying the CWA automatically to FOL ontologies reduces their ambiguity and more commonsense questions can be answered