Formal Verification of Runtime Compensation of Web Service Compositions: A Refinement and Proof Based Proposal with Event-B

One of the key interests in web services is the ability to compose them in order to build more powerful and complex ones running in an interoperable and distributed setting. Several languages, like BPEL, that describe such services have been proposed. Similarly to traditional complex systems, web service compositions may exhibit inappropriate behaviors in the presence of failures. Compensation mechanisms are available to express running services recovery in case of failures. This paper addresses the problem of the correct design of web service compositions in case of failures. It presents a novel correct-by-construction formal approach based on refinement using the Event-B method. The proposed approach defines a compensation mechanism to repair failed services at runtime. It addresses not only behavioral aspects but also, functional ones through the introduction of repairing invariants whose persistence is enforced during compensation at runtime. The proposal is illustrated relying on a case study.