A Typed Model for Multiparty Conversations

We present a type theory for analyzing concurrent multiparty interactions asfound in service-oriented computing, using the Conversation Calculus as under-lying model. Our theory introduces a novel and flexible type structure, able touniformly describe both the internal and the interface behavior of systems, re-ferred respectively as choreographies and contracts in web-services terminology.The notion of conversation builds on the fundamental concept of session, butgeneralizes it along directions up to now unexplored; in particular, conversationtypes discipline interactions in conversations while accounting for dynamicaljoin and leave of an unanticipated number of participants. We prove that well-typed systems never violate the prescribed conversation constraints. We alsopresent techniques to ensure progress of systems involving several interleavedconversations, a previously open problem.