Process Mediation in an Extended Roman Model

A mediator is a software module that provides sharing of services and and agglomeration of resources into complex services. Mediators will play a pivotal role in successful infrastructures for Semantic Web Services. Process mediation in Web Services involves issues of process compatibility and composability. Evolving standards of web services, such as the web service Execution Environment (WMSX [21]) focus mostly on compatibility issues in a B2B environment, whereas the problem of dynamic composition of web services is still maturing in the research community. In this paper we contribute to the composition aspect of process mediation. Web service process specification has reached well accepted standards, such as the Business Process Execution Language (BPEL4WS [9]). Moreover, it has recently been shown that process algebra provides a useful interpretation of BPEL specifications. Works such as [12, 19] provide the mapping from BPEL to process algebra, and show how the algebra can be used to describe Web Services during design stage. These works also demonstrate how process algebraic descriptions can be extracted from existing Web Services for reverse engineering purposes. This enables the use of numerous verification tools that are available for process algebra (e.g. LOTOS) in web service development. When it comes to the question of composability of web services some of the most fruitful results have been achieved within the Roman model [3, 2, 7, 11, 14, 5], an evolving framework that takes a highly computational approach to Web Service composition. In this paper we extend the Roman model by incorporating features from process algebra that will allow a fuller use of important functionalities of Web Services, such as parallelism, nondeterminism, and task decomposition. Our contributions are as follows: