The President:

Web services are software components that can be exposed on the internet and invoked using standard internet protocols. The syntactic properties of the interfaces of Web services are described using the Web Service Description Language WSDL [W3C, 2002a]. Research in semantic Web services aims at developing methods to describe the semantic and pragmatic aspects of Web services in addition to the syntactic aspects. These descriptions should permit formal reasoning about the capabilities of the published services, enabling software agents to interact automatically with services in order to accomplish certain defined goals. This thesis provides the following contributions to the field of semantic Web services: (i) It lays out a framework for capturing the semantics of Web service domains and presents the markup language SESMA, motivated by a critical analysis of existing work. SESMA is an XML-based format which allows the annotation of existing Web service and process descriptions with complementary information needed for automatic reasoning over Web services on the semantic level. (ii) To address heterogenous semantic service descriptions, which emerge as a consequence of the decentralization and lack of control over communication peers, the thesis puts forward a framework based on interschema knowledge for description logics that helps to resolve heterogeneity in service descriptions. (iii) The thesis provides an analysis and comparison of reasoning methods for the automatic selection and composition of Web services. Based on this analysis, it puts forward a three-layer framework for the development of automatic agents capable of solving problems in service-oriented computing domains. The framework augments formal reasoning methods (most notably AI planning methods) with mainstream programming techniques. The thesis gives an overview of a prototypical implementation of the proposed framework and provides an empirical evaluation of the presented solution.