Formal Specification of Correlation in WS Orchestrations Using BP-calculus

Correlation is an important mechanism used in orchestration languages for Web Services. It expresses means by which many instances of the same service can be carried on at the same time. In this paper we extend the BP-calculus, a language based on the π-calculus and dedicated to the specification of web service orchestrations, with a message algebra, a mechanism of function evaluation and a mechanism of correlation. The mechanism of function evaluation allows message handling while the mechanism of correlation guarantees uniqueness of service instances by preventing reception of messages inducing the same assignments of a correlation set. We also show how it can be used to express the semantics of the BPEL constructs coping with correlation. As an illustration of the usefulness of this process algebraic framework, we terminate with the presentation of a motivating example, the Trade Market example.