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. We present a novel combination of disjunctive logic programs under the answer set semantics with description logics for the Semantic Web. The combination is based on a well-balanced interface between disjunctive logic programs and description logics, which guarantees the decidability of the resulting formalism without assuming syntactic restrictions. We show that the new formalism has very nice semantic properties. In particular, it faithfully extends both disjunctive programs and description logics. Furthermore, we describe algorithms for reasoning in the new formalism, and we give a precise picture of its computational complexity. We also provide a special case with polynomial data complexity. 1

The realization of the Semantic Web vision, in which computational logic has a prominent role, has stimulated a lot of research on combining rules and ontologies, which are formulated in different formalisms, into a framework that is more useful for describing semantic content. In particular, combining logic programming with the Web Ontology Language (OWL), which is a standard based on description logics, emerged as an important issue for linking the Rules and Ontology Layers of the Semantic Web. Non-monotonic description logic programs (or dl-programs) were introduced for such a combination, in which a pair (L,P) of a description logic knowledge base L and a set of rules P with negation as failure is given a model-based semantics that generalizes the answer set semantics of logic programs. In this paper, we reconsider dl-programs and present a well-founded semantics for them as an analog for the other main semantics of logic programs. It generalizes the canonical definition of the well-founded semantics based on unfounded sets, and, as we show, lifts many of the well-known properties from ordinary logic programs to dl-programs. Among these properties: our semantics amounts to a partial model approximating the answer set semantics, which yields for positive and stratified dl-programs a total model coinciding with the answer set semantics; it has polynomial data complexity provided the access to the description logic

The Semantic Web languages RDFS and OWL have been around for some time now. However, the presence of these languages has not brought the breakthrough of the Semantic Web the creators of the languages had hoped for. OWL has a number of problems in the area of interoperability and usability in the context of many practical application scenarios which impede the connection to the Software Engineering and Database communities. In this paper we present OWL Flight, which is loosely based on OWL, but the semantics is grounded in Logic Programming rather than Description Logics, and it borrows the constraint-based modeling style common in databases. This results in di#erent types of modeling primitives and enforces a di#erent style of ontology modeling. We analyze the modeling paradigms of OWL DL and OWL Flight, as well as reasoning tasks supported by both languages. We argue that di#erent applications on the Semantic Web require di#erent styles of modeling and thus both types of languages are required for the Semantic Web.

Abstract. OWL DL corresponds to a Description Logic (DL) that is a fragment of classical first-order predicate logic (FOL). Therefore, the standard methods of automated reasoning for full FOL can potentially be used instead of dedicated DL reasoners to solve OWL DL reasoning tasks. In this paper we report on some experiments designed to explore the feasibility of using existing general-purpose FOL provers to reason with OWL DL. We also extend our approach to SWRL, a proposed rule language extension to OWL. 1

www.bell-labs.com/user/pfps/ Abstract. We discuss language architecture for the Semantic Web, and in particular different proposals for extending this architecture with a rules component. We argue that an architecture that maximises compatibility with existing languages, in particular RDF and OWL, will benefit the development of the Semantic Web, and still allow for forms of closed world assumption and negation as failure. Up until recent times it has been widely accepted that the architecture the Semantic Web will be based on a hierarchy of languages, each language both exploiting the features and extending the capabilities of the layers below. This has been famously illustrated in Tim Berners-Lee’s “Semantic Web Stack ” diagram [3] (see Figure 1). As a result of the work of the W3C Web Ontology Working Group, the “Ontology” layer has now been instantiated with the Web Ontology Language OWL [2]. Since then, attention has turned to the rules layer, and much effort has been devoted to the design of suitable rules languages. Perhaps influenced by some of this work, recently seen

In this paper, we present an ontology to represent the semantics of the IMS Learning Design (IMS LD) specification, a meta-language used to describe the main elements of the learning design process. The motivation of this work relies on the expressiveness limitations found on the current XML-Schema implementation of the IMS LD conceptual model. To solve these limitations, we have developed an ontology using Protégé at the knowledge level. In addition, we provide its implementation in OWL, the standard language of the Semantic Web, and the set of associated axioms in first-order logic. The OWL file is available at

Abstract. Using rules in conjunction with ontologies is a major challenge for the Semantic Web. We propose a pragmatic approach for reasoning with ontologies and rules, based on the Semantic Web standards and tools currently available. We first achieved an implementation of SWRL, the emerging OWL/RuleML-combining rule standard, using the Protégé OWL plugin. We then developed a Protégé plugin, SWRLJessTab, which enables to compute inferences with the Racer classifier and the Jess inference engine, in order to reason with rules and ontologies, both represented in OWL. A small example, including an OWL ontology and a SWRL rule base, shows that all the domain knowledge, i.e. the SWRL rule base and the OWL ontology, is required to obtain complete inferences. It illustrates that some reasoning support must be provided to interoperate between SWRL and OWL, not only syntactically and semantically, but also inferentially. 1.

Harold.Boley AT nrc-cnrc.gc.ca Abstract. In this paper we argue that a realistic architecture for the Semantic Web must be based on multiple independent, but interoperable, stacks of languages. In particular, we argue that there is a very important class of rule-based languages, with over thirty years of history and experience, which cannot be layered on top of OWL and must be included in the Semantic Web architecture alongside with the stack of OWL-based languages. The class of languages we are after includes rules in the Logic Programming style, which support default negation. We briefly survey the logical foundations of these languages and then discuss an interoperability framework in which such languages can co-exist with OWL and its extensions. 1

Abstract. MPEG-7 can be used to create complex and comprehensive metadata descriptions of multimedia content. Since MPEG-7 is defined in terms of an XML schema, the semantics of its elements have no formal grounding. In addition, certain features can be described in multiple ways. MPEG-7 profiles are subsets of the standard that apply to specific application areas, which can be used to reduce this syntactic variability, but they still lack formal semantics. In this paper, we propose an approach for expressing semantics explicitly by formalizing the semantic constraints of a profile using ontologies and rules, thus enabling interoperability and automatic use for MPEG-7 based applications. We demonstrate the feasibility of the approach by implementing a validation service for a subset of the semantic constraints of the Detailed Audiovisual Profile (DAVP). 1