Interface Input/Output Automata: Splitting Assumptions from Guarantees

We propose a new look at one of the most fundamental types of behavioral interfaces: discrete time specifications of communication---directly related to the work of de Alfaro and Henzinger [3]. Our framework is concerned with distributed non-blocking asynchronous systems in the style of Lynch's \IOAs [11], relying on a context dependent notion of refinement based on relativized language inclusion. There are two main contributions of the work. First, we explicitly separate assumptions from guarantees, increasing the modeling power of the specification language and demonstrating an interesting relation between blocking and non-blocking interface frameworks. Second, our composition operator is systematically and formally derived from the requirements stated as a system of inequalities. The derived composed interfaces are maximal in the sense of behavior, or equivalently are the weakest in the sense of assumptions. Finally, we present a method for solving systems of inequalities as used in our setup.