TUTORIAL ON MESSAGE SEQUENCE CHARTS

An introduction to the ITU standard language Message Sequence Chart (M SG) is provided. It is pointed out that MSC in many respects is comple mentary to the ITU specification and design language SDL. MSC in combi nation with SDL or other languages, now plays a role in nearly all sta ges of the system development process. Since MSC has been standardized in the same study group as SDL, the language form is quite analogous, e.g. it has a graphical (MSC/GR) and a textual (MSG/PR) syntax form. The MSC language in the present recommendation Z.120 (MSC'92), compris es basic language elements - instance, message, environment, action, t imer, process creation and termination, condition - and structural lan guage elements - ''coregion'' and ''submsc''. It is demonstrated how g lobal and non-global conditions may be used for the composition of MSC s. Whereas in MSC'92 the main emphasis is put on the elaboration of ba sic concepts and a corresponding formal semantics, in the new MSC vers ion (MSC'96) structural language constructs, essentially composition a nd object oriented concepts, will play a dominant role. With these new concepts, the power of MSC is enhanced considerably in order to overc ome the traditional restriction of MSC to the specification of few sel ected system runs.