The Pros and Cons of Netcharts

Abstract. Netcharts have been introduced recently by Mukund et al. in [17]. This new appealing approach to the specification of collections of message sequence charts (MSCs) benefits from a graphical description, a formal semantics based on Petri nets, and an appropriate expressive power. As opposed to high-level MSCs, any regular MSC language is the language of some netchart. Motivated by two open problems raised in [17], we establish in this paper that the questions (i) whether a given high-level MSC describes some netchart language (ii) whether a given netchart is equivalent to some high-level MSC (iii) whether a given netchart describes a regular MSC language are undecidable. These facts are closely related to our first positive result: We prove that netchart languages are exactly the MSC languages that are implementable by message passing automata up to refinement of message contents. Next we focus on FIFO netcharts: The latter are defined as the netcharts whose executions correspond to all firing sequences of their low-level Petri net. We show that the questions (i) whether a netchart is a FIFO netchart (ii) whether a FIFO netchart describes a regular MSC language (iii) whether a regular netchart is equivalent to some high-level MSC are decidable