Reliable Contracts for Unreliable Half-Duplex Communications

Recent trends in formal models of web services description languages and session types focus on the asynchronicity of communications. In this paper, we study a core of these models that arose from our modelling of the Sing# programming language, and demonstrate correspondences between Sing# contracts, asynchronous session behaviors, and the subclass of communicating automata with two participants that satisfy the half-duplex property. This correspondence better explains the criteria proposed by Stengel and Bultan for Sing# contracts to be reliable, and possibly indicate useful criteria for the design of WSDL. We moreover establish a polynomial-time complexity for the analysis of communication contracts under arbitrary models of asynchronicity, and we investigate the model-checking problems against LTL formulas.