A Survey of Web services Orchestration and Choreography with Formal Models

The service-oriented architecture (SOA) promises a new generation of information systems applications based on a new set of standards for enabling self-describing interoperable Web services. Web service orchestration and choreography are both concerned with the composition of Web services to meet the needs of business processes. There are two important standards for modeling and implementing workflows and business processes based on Web services: BPEL follows the orchestration paradigm, and WS-CDL covers the choreography. This paper gives a formal methods focused survey of BPEL and WS-CDL languages. Basic language constructs are presented as core building blocks for business processes. From the perspective of composing Web services to execute business processes, the orchestration is a more flexible approach compared to the choreography. For that reason we concentrate on some BPEL orchestration aspects using formal models: error, event, and compensation handling using extended version of π-calculus, correlation mechanisms using process algebra, and control flow constructs using Petri nets. All of the formal models allow the analysis and verification of BPEL processes what gives a good starting point for better understanding and further investigations on selected BPEL issues. This could also contribute towards the improvement of the quality of BPEL specification, the applicability of BPEL itself and the implementation of real orchestration engines.