describes the observable behavior of a Web service. When looking for Web services providing specific capabilities, the contract can be used as an important search key. This calls for a notion of contract equivalence that goes beyond nominal or structural equivalence.
In this paper we define a simple, yet expressive formal language for describing Web service contracts. We provide a natural, set-theoretic semantics of contracts and we use it for defining a family of equivalence relations that can be effectively used for discovering and adapting Web services implementing a specific contract.