From Finite State Communication Protocols to High-Level Message Sequence Charts

The ITU standard for MSCs provides a useful framework for visualizing communication protocols. HMSCs can describe a collection of MSC scenarios in early stages of system design. They extend nite state systems by partial order semantics and asynchronous, unbounded message exchange. Usually we ask whether an HMSC can be implemented, for instance by a nite state protocol. This question has been shown to be undecidable 5]. Motivated by the paradigm of reverse engineering we study in this paper the converse translation, speciically the question whether a nite state communication protocol can be transformed into an equivalent HMSC. This kind of translation is needed when e.g. diierent forms of speciica-tion (HMSC, nite automata, temporal logic) must be integrated into a single one, for instance into an HMSC. We show in this paper that translating nite state automata into HMSCs is feasible under certain natural assumptions. Speciically, we show that we can test in polynomial time whether a nite state protocol given by a B uchi automaton is equivalent to an HMSC, provided that the automaton satisses the diamond property (the precise bound is NLOGSPACE-complete). The diamond property is a natural property induced by con-currency. Under the weaker assumption of bounded B uchi automata we show that the test is co-NP-complete. Finally, without any buuer restriction the problem is shown to be undecidable.