Syntactic Analysis of Message Sequence Chart Specifications

Message Sequence Charts (MSCs) are gaining popularity in software engineering methods for concurrent and real-time systems. They are increasingly supported in software engineering tools to capture, for instance, system requirements, test scenarios, and simulation traces. MSCs have been standardized by ITU-T in Recommendation Z.120 [15]. However, various aspects of environment behavior remain underspeci ed in MSCs, e.g., the presence of resources for inter-process communication and the coordination of concurrent processes at points of control branching. Such underspeci cations can result in ambiguities in an MSC speci cation and discrepancies between an MSC speci cation and its implementation. In this paper we characterize two consequences of harmful underspeci cations: process divergence and non-local branching choice. We also present two syntax-based analysis algorithms that detect both problems. The syntactic characterization of these problems requires an MSC speci cation to be deadlock-free. Therefore, we also discuss deadlock detection in MSC speci cations. 2