One of the most challenging aspects in Web Service composition is guaranteeing transactional integrity. This is usually achieved by providing mechanisms for fault, compensation and termination (FCT) handling. WS-BPEL 2.0, the de-facto standard language for Business Process Orchestration provides powerful scope-based FCT-handling mechanisms. However, the lack of a formal semantics makes it difficult to understand and implement these constructs, and renders rigid analysis impossible. The general concept of compensating long-running business transactions has been studied in different formal theories, such as cCSP and Sagas, but none of them is specific to WS-BPEL 2.0. Other approaches aim at providing formal semantics for FCT-handling in WS-BPEL 2.0, but only concentrate on specific aspects. Therefore, they cannot be used for a comparative analysis of FCT-handling in WS-BPEL 2.0. In this paper we discuss the BPEL approach to FCT-handling in the light of recent research. We provide formal semantics for the WS-BPEL 2.0 FCT-handling mechanisms which aims at capturing the FCT-part of the WS-BPEL 2.0 specification in full detail. We then compare the WS-BPEL 2.0 approach to FCT-handling to existing formal theories.
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