Performance-Oriented Comparison of Web Services via Client-Specific Testing Preorders

The behavior of a Web service can be described by means of a contract, which is a specification of the legal interactions with the service. Given a repository of Web services, from the client viewpoint a proper service selection should be based on functional as well as non-functional aspects of the interactions. In this paper we provide a technique that enables a client both to discover compatible services and to compare them on the basis of specific performance requirements. Our technique, which is illustrated on a simple probabilistic calculus, relies on two families of client-specific probabilistic testing preorders. These are shown to be precongruences with respect to the operators of the language and not to collapse into equivalences unlike some more general probabilistic testing preorders appeared in the literature.