Modeling BPEL and BPEL4People with a Timed Interruptable pi-Calculus

Business Processing Execution Language (BPEL) and BPEL for People (BPEL4People) are two web services orchestration languages for composing web services. To describe formally their semantics, we introduce the π_it-calculus, a new variant of the π-calculus, in this paper. The good feature of the π_it-calculus is that its execution can be interrupted and can handle timing events as well. We provide both syntax and semantics of the π_it -calculus and define a strong bisimulation relation that specifies when two processes can be considered as the same. With the new calculus, we then model the activities of BPEL and BPEL4People, and give their precise semantics. Our formal framework may facilitate the reliability and consistency analysis in a BPEL or BPEL4People design process.