A New Logic-Based Approach for the Specification and Discovery of SemanticWeb Services

Matching Web services and client requirements in the form of goals is a significant challenge in the discovery of Semantic Web services. The most common but unsatisfactory approach to matching is set-based, where both the client and Web service declare what objects they require, and what objects they can provide. Matching then becomes the simple task of comparing sets of objects. This approach is inadequate because it says nothing about the functionality required by the client, or the functionality provided by the Web service. As a viable alternative to the set-based approach, in this thesis we use the F-Logic language as implemented in the FLORA-2 logic system to specify Web service capabilities and client requirements in the form of logic statements, clearly define what a match means in terms of logical inference, and implement a logic based discovery agent and matching engine using the FLORA-2 system. In order to be able to specify Semantic Web elements such as Web services, goals, ontologies, we define a sub-language of FLORA-2, which we call FLOG4SWS. The result is a practical, fully implemented matching engine and discovery agent based purely on logical inference for Web service discovery, with direct applicability to Web Service Modeling Ontology (WSMO) and Web Service Modeling Language (WSML), since F-Logic is intimately related to both. Before going to the implementation of new language (FLOG4SWS) and logical inference based discovery agent we investigate the strong as well as weak aspects of WSML in order to guide us in the search for a better alternative. In our studies into the theory of F-Logic, we discovered a mistake in the unification algorithm for F-Logic molecules, and we present a corrected version of the algorithm in this thesis as well.