Towards a Harmonization of UML-Sequence Diagrams and MSC

Sequence Diagrams as part of UML play an important role within use case driven object oriented (OO) software engineering. They can be seen as OO variants of the ITU-T standard language Message Sequence Chart (MSC) which is very popular mainly in the telecommunication area. Both notations would benefit from a harmonization. A more formal and powerful notation for Sequence Diagrams may arise, on the one hand. On the other hand, the application area of MSC might be considerably enlarged. In this context, it has to be noted that the acceptance of a language in the OO community essentially depends on a clear visualization of constructs typical for OO modelling. It is argued that Sequence Diagrams can be transformed into MSC diagrams if some enhancements of MSC are introduced. Such a transformation demonstrates the big advantage of MSC concerning composition mechanisms, particularly, in comparison with the rather obscuring branching constructs in Sequence Diagrams. At the same time, such a transformation may be used for a formalization of Sequence Diagrams in UML since MSC has a formal semantics based on process algebra.