Protocol contracts with application to choreographed multiparty collaborations

E-commerce collaborations and cross-organizational workflow applications are increasingly attractive given the universal connectivity provided by the Internet. Such applications are inherently concurrent and non-deterministic, so standard software engineering practices are inadequate, and we need new techniques to design extended collaborations and ensure that the implemented designs will behave correctly. The emerging technique for achieving this is to use a choreography, a global description of the possible sequencing of message exchange between the participants, as the basis for both the design of the collaboration and verification of its behavior. We describe a new technique that uses compositions of partial descriptions to define a choreography and show how the technique can be used to model the use of data and computation in the rules of the collaboration. We define conditions for correctness and show that they can be applied separately to each partial description. We demonstrate the expressive power of the technique with examples and discuss how it improves on previously published approaches.