Abstract. We think of Match as an operator which takes two graph-like structures and produces a mapping between semantically related nodes. We concentrate on classifications with tree structures. In semantic matching, correspondences are discovered by translating the natural language labels of nodes into propositional formulas, and by codifying matching into a propositional unsatisfiability problem. We distinguish between problems with conjunctive formulas and problems with disjunctive formulas, and present various optimizations. For instance, we propose a linear time algorithm which solves the first class of problems. According to the tests we have done so far, the optimizations substantially improve the time performance of the system. 1.

Abstract. While current approaches to ontology mapping produce good results by mainly relying on label and structure based similarity measures, there are several cases in which they fail to discover important mappings. In this paper we describe a novel approach to ontology mapping, which is able to avoid this limitation by using background knowledge. Existing approaches relying on background knowledge typically have one or both of two key limitations: 1) they rely on a manually selected reference ontology; 2) they suffer from the noise introduced by the use of semi-structured sources, such as text corpora. Our technique circumvents these limitations by exploiting the increasing amount of semantic resources available online. As a result, there is no need either for a manually selected reference ontology (the relevant ontologies are dynamically selected from an online ontology repository), or for transforming background knowledge in an ontological form. The promising results from experiments on two real life thesauri indicate both that our approach has a high precision and also that it can find mappings, which are typically missed by existing approaches.

The increasing awareness of the benefits of ontologies for information processing has lead to the creation of a number of large ontologies about real world domains. The size of these ontologies and their monolithic character cause serious problems in handling them. In other areas, e.g. software engineering, these problems are tackled by partitioning monolithic entities into sets of meaningful and mostly self-contained modules. In this paper, we suggest a similar approach for ontologies. We propose a method for automatically partitioning large ontologies into smaller modules based on the structure of the class hierarchy. We show that the structure-based performs surprisingly well on real world ontologies.

Abstract. The paper addresses the problem of reasoning with multiple ontologies interrelated with semantic mappings. This problem is becoming more and more relevant due to the necessity of building a scalable ontological reasoning tools for the Semantic Web. In contrast to the so called global approach, in which reasoning with multiple semantically related ontologies is performed in a global knowledge base that encodes both ontologies and semantic mappings, we propose a distributed reasoning approach in which reasoning is the result of combination via semantic mappings of local reasonings chunks performed in single ontologies. The paper presents a tableau-based distributed reasoning procedure which is sound and complete w.r.t. Distributed Description Logics, the formal framework used to represent multiple semantically connected ontologies. The paper also describes the design and implementation principles of a distributed reasoning system, called DRAGO (Distributed Reasoning Architecture for a Galaxy of Ontology), that implements such distributed decision procedure. 1

Abstract. The standardization of the second generation Web Ontology Language, OWL, leaves a crucial issue for Web-based ontologies unsatisfactorily resolved: how to represent and reason with multiple distinct, but linked, ontologies. OWL provides the owl:imports construct which, roughly, allows Web ontologies to include other Web ontologies, but only by merging all the linked ontologies into a single logical “space. ” Recent work on multidimensional logics, fusions and other combinations of modal logics, distributed and contextual logics, and the like have tried to find formalisms wherein knowledge bases (and their logic) are kept more distinct but yet affect each other. These formalisms have various degrees of robustness in their computational complexity, their modularity, their expressivity, and their intuitiveness to modelers. In this paper, we explore a family of such formalisms, grounded in E-connections as extensions to OWL, with emphasis on a novel sub-formalism that seems very straightforward to implement on existing tableau OWL reasoners, as witnessed by our implementation of this formalism in the OWL reasoner Pellet. We discuss how to integrate those formalisms into OWL, as well as some of the issues that modelers have to face when using such formalisms in the context of a large number of heterogeneous, independently developed, richly interconnected ontologies that we expect to be the norm on the Semantic Web. 1

We investigate a formalism for reasoning with multiple local ontologies, connected by directional semantic mappings. We propose: (1) a relatively small change of semantics which localizes inconsistency (thereby making unnecessary global satisfiability checks), and preserves directionality of “knowledge import”; (2) a characterization of inferences using a fixed-point operator, which can form the basis of a cache-based implementation for local reasoners; (3) a truly distributed tableaux algorithm for cases when the local reasoners use subsets of SHIQ. Throughout, we indicate the applicability of the results to several recent proposals for knowledge representation and reasoning that support modularity, scalability and distributed reasoning. 1

Abstract. Modular ontology languages, such as Distributed Description Logics (DDL), E-connections and Package-based Description Logics (P-DL) offer two broad classes of approaches to connect multiple ontology modules: the use of mappings or linkings between ontology modules e.g., DDL and E-connections; and the use of importing e.g., P-DL. The major difference between the two approaches is on the usage of “foreign terms ” at the syntactic level, and on the local model disjointness at the semantic level. We compare the semantics of linking in DDL and E-connections, and importing in P-DL within the Distributed First Order Logics (DFOL) framework. Our investigation shows that the domain disjointness assumption adopted by the linking approach leads to several semantic difficulties. We explore the possibility of avoiding some of these difficulties using the importing approach to linking ontology modules. 1

Abstract. We show that the Semantic Web needs a formal semantics for the various kinds of links between ontologies and other documents. We provide a model theoretic semantics that takes into account ontology extension and ontology versioning. Since the Web is the product of a diverse community, as opposed to a single agent, this semantics accommodates different viewpoints by having different entailment relations for different ontology perspectives. We discuss how this theory can be practically applied to RDF and OWL and provide a theorem that shows how to compute perspective-based entailment using existing logical reasoners. We illustrate these concepts using examples and conclude with a discussion of future work. 1

Abstract. Knowledge representation formalisms used on the Semantic Web adhere to a strict open world assumption. Therefore, nonmonotonic reasoning techniques are often viewed with scepticism. Especially negation as failure, which intuitively adopts a closed world view, is often claimed to be unsuitable for the Web where knowledge is notoriously incomplete. Nonetheless, it was suggested in the ongoing discussions around rules extensions for languages like RDF(S) or OWL to allow at least restricted forms of negation as failure, as long as negation has an explicitly defined, finite scope. Yet clear definitions of such “scoped negation ” as well as formal semantics thereof are missing. We propose logic programs with contexts and scoped negation and discuss two possible semantics with desirable properties. We also argue that this class of logic programs can be viewed as a rule extension to a subset of RDF(S). 1

The need to represent mappings between different ontologies has been recognized as a result of the fact that different ontologies may partially overlap, or even represent the same domain from different points of view. Unlike ontology languages, work on languages to represent ontology mappings has not yet reached a state where a common understanding of the basic principles exists. In this paper we propose a formal comparison of existing mapping languages by translating them into distributed first order logic. This allows us to analyze underlying assumptions and differences in the interpretation of ontology mappings. 1