On Nets with Structured Concurrency

An extension of Petri nets with a statechart-like AND/OR state hierarchy is defined and studied. The resulting net variant, statechart nets, is shown to coincide, under certain conditions, with a strict subclass of safe nets in which concurrency is structured. Next, syntactic constraints on statechart nets are defined that guarantee absence of deadlocks and livelocks. Such syntactic constraints are hard to give for ordinary Petri nets. Together, these results give more insight into the expressive power and usefulness of AND/OR state hierarchies, and into the differences between statecharts and Petri nets.