Reasoning about Channel Passing in Choreography

Web services choreography describes global models of service interactions among a set of participants. For an interaction to be executed, the participants must know the required channel(s) used in the interaction, otherwise the execution will get stuck. Because of dynamic composition, the initial channel set on each participant is often insufficient to meet the requirements. It is the responsibility of the participants to pass required channels owned (known) by one to some others. Since a choreography may involve many participants and complex channel constraints, it is hard for designers to specify channel passing in a choreography exactly as required. In this paper, we address the problem of checking whether a choreography lacks channels or has redundant channels, and how to automatically generate channel passing based on interaction flows of the choreography in the case of channel absence. Concretely, we propose a small language Chor_c named for a channel interaction sub-language for modeling the channel passing aspect of choreography. Based on the formal operational semantics of Chor_c, the algorithms for static checking choreography and generating channel passing are studied as well.