Operational and Compositional Semantics of Synchronous Automaton Compositions

The state/transition paradigm has been used extensively for the description of event-driven, parallel systems. However, the lack for hierarchic structure in such descriptions usually prevents us from using this paradigm in a real programming language. We propose the Argos language for reactive systems. The basic components of a program are input/output-labeled transition systems verifying reactivity (a property similar to input-enabling in IO-automata). The composition operations (parallel composition and reenement, providing hierarchy) are based upon the synchronous broadcast mechanism of Esterel. We deene the language formally in an algebraic framework, and give an operational semantics. The main result is the compositionality of the semantics; we prove that the bisimulation of models induces an equivalence which is a congruence for the operators we propose. An interesting point is the way we introduce hierarchy in a compositional way.