Stepwise Design with Message Sequence Charts

Use cases are useful in various stages of the software process. They are very often described using text that has to be interpreted by system designers. This could lead to implementation errors. Another drawback of using such informal notations is that automating the process of moving from use cases to design specification is difficult, if not impossible. It would be beneficial to represent use cases in an unambiguous way, thereby reducing the probability of misunderstanding and allowing for automation of various activities in the software process. Message Sequence Charts (MSC) is a formal language and widely used in telecommunications for the specification of the required behaviors. In this paper, we use MSC for describing use cases and we propose an approach for stepwise refinement from high-level use cases in MSC to design MSCs that contain more details about the internal components of the system and their interactions. The refinement steps are done by the designer and guided by the system architecture. For each step, the newly obtained MSC is validated automatically against the previous MSC using a conformance relation between MSCs.