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The ability to extract meaningful fragments from an ontology is essential for ontology reuse. We propose a definition of a module that guarantees to completely capture the meaning of a given set of terms, i.e., to include all axioms relevant to the meaning of these terms. We show that the problem of determining whether a subset of an ontology is a module for a given vocabulary is undecidable even for OWL DL. Given these negative results, we propose sufficient conditions for a for a fragment of an ontology to be a module. We propose an algorithm for computing modules based on those conditions and present our experimental results on a set of real-world ontologies of varying size and complexity.

We present a novel approach to probabilistic description logic programs for the Semantic Web in which disjunctive logic programs under the answer set semantics are tightly coupled with description logics and Bayesian probabilities. The approach has several nice features. In particular, it is a logic-based representation formalism that naturally fits into the landscape of Semantic Web languages. Tightly coupled probabilistic description logic programs can especially be used for representing mappings between ontologies, which are a common way of approaching the semantic heterogeneity problem on the Semantic Web. In this application, they allow in particular for resolving inconsistencies and for merging mappings from different matchers based on the level of confidence assigned to different rules. Furthermore, tightly coupled probabilistic description logic programs also provide a natural integration of ontologies, action languages, and Bayesian probabilities towards Web Services. We explore the computational aspects of consistency checking and query processing in tightly coupled probabilistic description logic programs. We show that these problems are decidable and computable, respectively, and that they can be reduced to consistency checking and cautious/brave reasoning, respectively, in tightly coupled disjunctive description logic programs. Using these results, we also provide an anytime algorithm for tight query processing. Furthermore, we analyze the complexity of consistency checking and query processing in the new probabilistic description logic programs, and we present a special case of these problems with polynomial data complexity. © 2009 Springer Berlin Heidelberg.

Virtual Reality (VR) allows creating interactive three-dimen sional computer worlds in which objects have a sense of spatial and physical presence and can be manipulated by the user as such. Different software tools have been developed to build virtual worlds. However, most tools require considerable background knowledge about VR and the virtual world needs to be expressed in low-level VR primitives. This is one of the reasons why developing a virtual world is complex, time-consuming and expensive. Introducing a conceptual design phase in the development process will reduce the complexity and provides an abstraction layer to hide the VR implementation details. However, virtual worlds contain features not present in classical software. Therefore, new modeling concepts, currently not available in classical conceptual modeling languages, such as ORM or UML, are required. Next to introducing these new modeling concepts, it is also necessary to define their semantics to ensure unambiguousness and to allow code generation. In this paper, we introduce conceptual modeling concepts to specify complex connected 3D objects. Their semantics are defined using F-logic, a full-fledged logic following the object-oriented paradigm. F-logic will allow applying reasoners to check the consistency of the specifications and to investigate properties before the application is actually built.

We introduce a novel view on how to deal with the problems of semantic interoperability in distributed systems. This view is based on the concept of emergent semantics, which sees both the representation of semantics and the discovery of the proper interpretation of symbols as the result of a self-organizing process performed by distributed agents exchanging symbols and having utilities dependent on the proper interpretation of the symbols. This is a complex systems perspective on the problem of dealing with semantics. We highlight some of the distinctive features of our vision and point out preliminary examples of its application.

This article presents a technique to incrementally maintain materializations of ontological entailments. Materialization consists in precomputing and storing a set of implicit entailments, such that frequent and/or crucial queries to the ontology can be solved more efficiently. The central problem that arises with materialization is its maintenance when axioms change, viz. the process of propagating changes in explicit axioms to the stored implicit entailments. When considering rule-enabled ontology languages that are operationalized in logic databases, we can distinguish two types of changes. Changes to the ontology will typically manifest themselves in changes to the rules of the logic program, whereas changes to facts will typically lead to changes in the extensions of logical predicates. The incremental maintenance of the latter type of changes has been studied extensively in the deductive database context and we apply the technique proposed in [30] for our purpose. The former type of changes has, however, not been tackled before. In this article we elaborate on our previous papers [32, 33], which extend the approach of [30] to deal with changes in the logic program. Our approach is not limited to a particular ontology language but can be generally applied to arbitrary ontology languages that can be translated to Datalog programs, i.e. such as O-Telos, F-Logic [16] RDF(S), or Description Logic Programs [34]. © Springer-Verlag Berlin Heidelberg 2004.

This paper describes a semi-automatic transformation from object-oriented conceptual models to logical theories. By associating a logical theory with a conceptual model, we are able to combine the best of both worlds. On one hand, the object-oriented software development paradigm is recognized to be well-suited to build maintainable and-communicable conceptual models. On the other hand, the logical programming paradigm offers very powerful and semantically founded concepts to represent knowledge and the use of logical inference systems makes it possible to prototype solutions to computational tasks: Since our method makes this mapping from conceptual models to logical theories traceable, dealing with the evolution of the problem domain and requirements becomes more manageable. Moreover a path is offered towards building prototypes for object-oriented conceptual models. ispartof: pages:152-166 ispartof: Lecture Notes in Computer Science vol:2503 pages:152-166 ispartof: 21th International Conference on Conceptual Modeling (ER 2002) location:Tampere, Finland date:7 Oct - 11 Oct 2002 status: published

Current Web Modelling Languages (WMLs) fall short of the requirements for the modelling of web system development. In particular, those WMLs with a hypermedia basis are more closely focussed on the information architecture whereas software WMLs are more focussed on the functional architecture. Generally, modelling languages have failed to bridge the gap between these two areas, nor do they handle well the connection between different levels of abstraction and are largely unable to connect well with business models. Based on an analysis of existing modelling approaches, we propose a conceptual extension to modelling approaches that attempts to address these limitations. We show how it can implemented using UML modelling along with the addition of concepts taken fromWeb information modelling approaches, WebML in particular. The extensions are structured around the model-view-controller concept, which we argue provides an appropriate integrating modelling framework. We begin by discussing the scope and objectives of the extensions, followed by the extensions themselves. We then illustrate the extensions using a small case study.

The objective of this study is to provide a dynamic spatial view model to Geographical Information Systems. The notion of spatial view allows independent external interpretations of a database schema i.e. the representation of geographical data according to different point of views and in function of objectives which may be distinct from those of the database schema. As no view definition has been offered for spatial data, this research proposes the definition of a view formalism for spatial databases.The model we develop is defined as an extension of the classic database view. Spatial views model both alphanumeric and spatial data. A spatial view is defined an ordered set of spatial view atoms. Each atom is a set of database relations, a set of conventional spatial and non spatial database operators. Manipulations of views allow the derivation of new views according to specific needs. They are realized with a set of identified operators. The spatial view model integrates structured and cognitive spatial representations. The proposal defines a model and operations that allow the decomposition and representation of navigation knowledge. The spatial view allows a displacement action to be situated within its geographical context through complementary abstraction levels that accept partial knowledge. It associates the description of a route with related multidimensional spaces including significant symbolic landmarks and textual descriptions. Continuity of route representation is ensured by the graph concept applied to spatial views and spatial collage spatially materialized by connections. A route trace in each spatial view spaces is described by a section. Graph operators allow abstraction level changes within the route representation.The spatial view concept provides a relative flexibility to compose a land representation adapted to user needs. From the external modeling point of view, the spatial view concept enables representation of different, numerous database schema interpretations which are inevitable in GIS applications. By extension, it facilitates schema evolution by allowing external representations which do not directly affect the original database schema. For geographic applications, spatial views gives an original solution for database consultation and manipulation tasks; L'objectif de cette étude est la définition d'un modèle de vue spatiale dynamique adapté aux Systèmes d'Information Géographiques. La notion de vue spatiale proposée permet une relative indépendance dans l'interprétation d'un schéma de base de données spatiales à savoir la représentation de données géographiques selon différents points de vues et en fonction d'objectifs distincts de ceux du schéma d'origine. Les mécanismes classiques de vue, dans le domaine des bases de données, n'intégrant pas la composante spatiale, cette recherche propose la définition d'un formalisme de vue adapté aux bases de données spatiales.Le modèle proposé est défini comme une extension de la vue classique telle qu'elle est identifiée par les bases de données. Le modèle de vue spatiale intègre la représentation de données spatiales et non spatiales. Une vue spatiale est un ensemble ordonné d'atomes de vue spatiale. Chaque atome de vue spatiale est construit à partir de relations et d'opérateurs spatiaux et non spatiaux. Un ensemble d'opérateurs de manipulation de vues spatiales est défini. Ces opérateurs permettent la manipulation et la dérivation de nouvelles vues spatiales.La vue spatiale autorise la représentation de modèles spatiaux structurés et cognitifs. La proposition définit un modèle et les opérations qui permettent la décomposition et la représentation d'un processus de déplacement. Le modèle de vue spatiale permet de situer la représentation d'un déplacement dans son contexte géographique à partir de niveaux d'abstraction complémentaires qui intègrent des connaissances partielles. Il associe la description d'un processus de déplacement dans un contexte d'espaces multi-dimensionels. La continuité de la représentation d'un déplacement est assurée par l'application de constructeurs de graphe appliqués au cadre de la vue spatiale à travers des concepts de collages et de connexions de vues spatiales. L'application d'opérateurs de graphe permet des changements de niveau d'abstraction dans la représentation des processus navigationnels.La vue spatiale apporte une flexibilité aux utilisateurs dans la représentation de données géographiques. Du point de vue de la modélisation, la vue spatiale permet la représentation de différentes interprétations utilisateurs d'une base de données spatiales. Par extension, la vue spatiale facilite l'évolution du schéma des bases de données spatiales. Elle constitue une forme originale de manipulation et de consultation d'applications géographiques.

Until recently, most data interoperability techniques involved central components, e.g., global schemas or ontologies, to overcome semantic heterogeneity for enabling transparent access to heterogeneous data sources. Today, however, with the democratization of tools facilitating knowledge elicitation in machine-processable formats, one cannot rely on global, centralized schemas anymore as knowledge creation and consumption are getting more and more dynamic and decentralized. Peer Data Management Systems (PDMS) implementing semantic overlay networks are a good example of this new breed of systems eliminating the central semantic component and replacing it through decentralized processes of local schema alignment and query processing. As a result semantic interoperability becomes an emergent property of the system. In this talk we provide examples of both structural and dynamic aspects of such emergent semantics systems based on semantic overlay networks. ?From the structural perspective we can show that the typical properties of self-organizing networks also appear in semantic overlay networks. They form directed, scalefree graphs. We present both analytical models for characterizing those graphs and empirical results providing insight on their quantitative properties. Then we present semantic gossiping, a model for the dynamic reorganization of semantic overlay networks resulting from information propagation through the network and local realignment of semantic relationships. The techniques we apply in that context are based on belief propagation, a distributed probabilistic reasoning technique frequently encountered in self-organizing systems. Finally we will give a quick glance on how this techniques can be implemented at the systems level, based on a peer-to-peer systems approach.