Abstract
In this paper, we present the WebComposer tool for the automatic composition and execution of Web Service-based workflows. We use ontologies to describe and browse workflows. We associate messages and operations with workflow domain concepts using WSDL extensibility. The automatic workflow implementation through WebComposer enables the full separation of the workflow logic and the implementation technology. WebComposer provides the execution of ad-hoc programs by users and the automatic maintenance of these programs, as the available Web services are altered.