Abstract
Web Service composition has become increasingly important with more and more Web Services developed and deployed on the Web. It requires a formal and clear representation for analysis, design, and implementation. The Business Process Execution Language for Web Service (BPEL4WS), which is an XML-based language, provides a good basis to describe Web Service composition. However, it still lacks a formal, explicit and graphic representation for visual modeling of the composition process and result. The Object-Process Methodology (OPM) has been shown to successfully describe the structure and behavior of systems using an integrated and coherent set of Object-Process Diagrams (OPDs). It should also be suitable to describe Web Service composition. In this paper we will discuss the extensions which are necessary to OPM in order to describe Web Service composition. We propose several mapping rules between BPEL4WS and OPD that are identical to the rules between Object-Process Language (OPL) and OPD so that the OPD set can be automatically created from existing BPEL4WS documents and BPEL4WS documents can be generated from the OPD set automatically, with some manual work. With the visual and explicit representation of Web Service composition, it will make the design and implementation of the composed services easier and more comprehensive.