Local liveness for 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 specified 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 verification of live transition systems. Second, while machine closure and receptiveness are based on infinite games, locality is based on repeated finite games, and thus easier to check. Third, no expressive power is lost by the restriction to local liveness conditions. We illustrate the appeal of local liveness using the model of Fair Reactive Systems, a nonblocking trace model of communicating processes.