Ad-hoc invocation of semantic Web services

We present the Web service description framework (WSDF), which provides both a representation mechanism and a runtime system architecture for semantically enriched Web Services. We analyze existing languages such as BPEL4WS and OWL-S before addressing their deficiencies in our proposal. Our approach allows a client to invoke a service based solely on a shared ontology, i.e. without prior knowledge on the API, providing an important building block towards a global, flexible information infrastructure. Another main point is that WSDF can be applied to clients and services written in a conventional object oriented programming language. This is achieved by lifting data structures to an ontology level in which rich logical statements about services can be formalized. We also present a detailed system architecture that covers planning, invocation, and the automatic processing of the service results, which is accomplished using the observer design pattern and by asserting the result in the respective model. Furthermore, the required annotations can be specified conveniently by placing comments in the source code.