Putting Extended Sequence Charts to Practice

Within the SDL-User-Guidelines only a short section is devoted to Sequence Charts (SC) as one of the auxiliary diagrams. However within an integrated tool set for design of real time systems, particularly telecommunication systems, SC's may very well play an important role. The power of SC's shows up even if the pure message form (standard form) is extended by some additional concepts, mainly coming from SDL-process diagrams. Eventually one trace in an SDL-system can be described completely by an extended SC. The main importance of SC's, providing a graphically transparent description of system behaviour, lies in the stage of requirement definition. All later stages in system design have to be shown to be consistent with the SC's, set up for requirement definition. Thus SC's also provide a basis for test cases of the later implemented system. Beyond that, a stepwise refinement of SC's offers a realistic chance for a systematic computer aided and user guided construction of SDL-process diagrams from SC's. A discussion of the role of SC's within the whole software lifecycle is presented in chapter 1. In chapter 2 several variants of SC's are introduced providing a stepwise refinement of the pure message form. Chapter 3 is devoted to the semantics of SC's particularly to the (time)ordering of SC-events. Finally in chapter 4 the realization of the presented methodology within an integrated set of tools for software design is elucidated.