Compositional Modeling of Fair Reactive Systems ?

We argue that the standard constraints on liveness conditions in nonblocking trace models|machine closure for closed systems, and receptiveness for open systems|are unnecessarily weak and complex , and that liveness should, instead, be speciied by augmenting transition systems with acceptance conditions that satisfy a locality constraint. First, locality implies machine closure and receptiveness, and thus permits the composition and modular veriication of live transition systems. Second, while machine closure and receptiveness are based on innnite games, locality is based on repeated nite games, and thus easier to check. Third, no expressive power is lost by the restriction to local live-ness conditions. We illustrate the appeal of local liveness using the model of Fair Reactive Systems, a nonblocking trace model of communicating processes.