Ontologies are shared models of a domain that encode a view which is common to a set of different parties. Contexts are local models that encode a party's subjective view of a domain. In this paper we show how ontologies can be contextualized, thus acquiring certain useful properties that a pure shared approach cannot provide. We say that an ontology is contextualized or, also, that it is a contextual ontology, when its contents are kept local, and therefore not shared with other ontologies, and mapped with the contents of other ontologies via explicit (context) mappings. The result is Context OWL (C-OWL), a language whose syntax and semantics have been obtained by extending the OWL syntax and semantics to allow for the representation of contextual 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

In this paper, we propose a set of tasks that are relevant for the modular reuse of ontologies. In order to formalize these tasks as reasoning problems, we introduce the notions of conservative extension, safety and module for a very general class of logic-based ontology languages. We investigate the general properties of and relationships between these notions and study the relationships between the relevant reasoning problems we have previously identified. To study the computability of these problems, we consider, in particular, Description Logics (DLs), which provide the formal underpinning of the W3C Web Ontology Language (OWL), and show that all the problems we consider are undecidable or algorithmically unsolvable for the description logic underlying OWL DL. In order to achieve a practical solution, we identify conditions sufficient for an ontology to reuse a set of symbols “safely”—that is, without changing their meaning. We provide the notion of a safety class, which characterizes any sufficient condition for safety, and identify a family of safety classes–called locality—which enjoys a collection of desirable properties. We use the notion of a safety class to extract modules from ontologies, and we provide various modularization algorithms that are appropriate to the properties of the particular safety class in use. Finally, we show practical benefits of our safety checking and module extraction algorithms. 1.

Abstract. The task of building an open and scalable ontology browsing and editing tool based on OWL, the first standardized Web-oriented ontology language, requires the rethinking of critical User Interface and ontological engineering issues. In this paper, we describe Swoop, a browser and editor specifically tailored to OWL ontologies. Taking a ”Web view” of things has proven quite instructive and we discuss some insights into Web Ontologies that we gained through our experience with Swoop, including issues related to the display, navigation, editing and collaborative annotation of OWL ontological data.

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

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

Abstract. In the extensive usage of ontologies envisaged by the Semantic Web there is a compelling need for expressing mappings between the components of heterogeneous ontologies. These mappings are of many different forms and involve the different components of ontologies. State of the art languages for ontology mapping enable to express semantic relations between homogeneous components of different ontologies, namely they allow to map concepts into concepts, individuals into individuals, and properties into properties. Many real cases, however, highlight the necessity to establish semantic relations between heterogeneous components. For example to map a concept into a relation or vice versa. To support the interoperability of ontologies we need therefore to enrich mapping languages with constructs for the representation of heterogeneous mappings. In this paper, we propose an extension of Distributed Description Logics (DDL) to allow for the representation of mapping between concepts and relations. We provide a semantics of the proposed language and show its main logical properties. 1

Abstract. Lightweight ontologies in the form of RDF vocabularies such as SIOC, FOAF, vCard, etc. are increasingly being used and exported by “serious ” applications recently. Such vocabularies, together with query languages like SPARQL also allow to syndicate resulting RDF data from arbitrary Web sources and open the path to finally bringing the Semantic Web to operation mode. Considering, however, that many of the promoted lightweight ontologies overlap, the lack of suitable standards to describe these overlaps in a declarative fashion becomes evident. In this paper we argue that one does not necessarily need to delve into the huge body of research on ontology mapping for a solution, but SPARQL itself might — with extensions such as external functions and aggregates — serve as a basis for declaratively describing ontology mappings. We provide the semantic foundations and a path towards implementation for such a mapping language by means of a translation to Datalog with external predicates.

For many years, the Modal Logic community has pursued various techniques for robustly combining logics. These methodologies reflect a new direction in Logic applied to Knowledge Representation, namely the direction toward constructing and investigating complex combined logical formalisms out of simpler ones. The E-Connections framework is a novel technique for combining Abstract Description Systems (ADSs), a generalization of several families of decidable logics, including Description Logics, Modal Logics, as well as many logics of time and space. In this paper, we investigate different E-Connection languages involving Description Logics. Recently, E-Connections of Description Logics have been proposed as a suitable formalism for various applications, such as ontology integration on the Semantic Web. We propose two novel combinations: one-way E-Connections and E-Connections allowing for transitive and symmetric link relations. Then, we investigate in depth the problem of reasoning with E-Connections and provide different tableau-based decision procedures. Finally, we show that our algorithms can be implemented as an extension of existing DL reasoners and present our prototype implementation in the Pellet system. To the best of our knowledge, the algorithms presented in this paper are the first practical decision procedures for E-Connections. 1