We present XPi, a core calculus for XML messaging. XPi features asynchronous communications, pattern matching, name and code mobility, integration of static and dynamic typing. Flexibility and expressiveness of this calculus are illustrated by a few examples, some concerning description and discovery of web services. In XPi, a type system disciplines XML message handling at the level of channels, patterns, and processes. A run-time safety theorem ensures that in well-typed systems no service will ever receive documents it cannot understand, and that the offered services, even if redefined , will be consistent with the declared channel capacities. This work has been partially supported by EU within the IST FET-Global Computing initiative, projects MIKADO and PROFUNDIS.
Abstract. In the context of service-oriented computing, behavioural contracts are abstract descriptions of the message-passing behaviour of services. They can be used to check properties of service compositions such as, for instance, clientservice compliance. Previous formal models for contracts consider unidirectional send and receive operations. In this paper, we present two models for contracts with bidirectional request-response operations, in the presence of unboundedly many instances of both clients and servers. The first model takes inspiration from the abstract service interface language WSCL, the second one is inspired by Abstract WS-BPEL. We prove that client-service compliance is decidable in the former while it is undecidable in the latter, thus showing an interesting expressiveness gap between the modeling of request-response operations in WSCL and in Abstract WS-BPEL.
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