Compositional Message Sequence Charts
01 January 2001
Message sequency charts (MSCs) is a standard notation for describing the interaction between communicating objects. It is popular among the designers of communication protocols. MSCs enjoy both a visual and a textual representation. High level MSCs (HMSCs) allow specifying infinite scenarios and different choices. In this paper we demonstrate a weakness of HMSCs, which disallows one to model certain interactions. Specifically, an HMSC consists of a graph, where each node is a finite MSC with matched send receive events, and vice versa. The corresponding graph notation will be called HCMSC. We will show, by means of an example, that some simple finite state and simple communication protocol cannot be represented using HMSCs. We then propose an extension to the MSC standard, which allows HMSC nodes to include unmatched messages. With the extended framework, we provide an algorithm for automatically constructing an MSC representation for finite state asynchronous message passing protocols.