Structured Operational Semantics for Concurrency and Hierarchy

This paper presents a language, CHA, and semantics for studying Statecharts-like drawings. CHA is a process algebra. CHA terms are interpreted as programs that extend Mealy-style nite automata with concurrent execution and hierarchical structure. Transitions in CHA can cross hierarchy boundaries, and it is this fact that makes giving a semantics to CHA (and to Statecharts) an interesting problem. In the terminology of Mil89] all of the function symbols in CHA except the constants are static combinators. CHA is given an operational semantics in the Structural Operational Semantics (SOS) style of Plotkin Plo81]. The Transition System Speciication (TSS) methodology of GV88] is employed, and the TSS presented is in the tyf t=tyxt format from that paper. Conformance to the tyf t=tyxt format has several beneets for analyzing CHA, the most important of which is that bisimulation is a congruence in the Labeled Transition System (LTS) C of the language.