Interaction of finite state machines and concurrency models

Hierarchical concurrent finite state machines (HCFSMs) dramatically increase the usability of finite state machines (FSMs). However, most formalisms that support HCFSMs, such as statecharts (and its variants), tightly integrate the concurrency semantics with the FSM semantics. We, in contrast, allow FSMs to be hierarchically combined with multiple concurrency models, enabling selection of the most appropriate concurrency semantics for the problem at hand. A key issue for the success of this scheme is to define how FSMs interact with various concurrency models without ambiguities. We focus on the interaction of FSMs and three concurrency models: synchronous data-flow, discrete-event and synchronous/reactive models.