UML, The Future Standard Software Architecture Description Language?

The object-oriented Unified Modeling Language (UML) which has become OMG standard offers a great variety of concepts for the definition of the structure and the expected behavior of a software system. It has the potential to replace many previously used software architecture description languages. This is especially true for the subset of so-called module interconnection languages. Compared with these languages UML has the main drawback that its module concept is continuously changing from version to version without reaching a well-defined stable state (until the current version 1.3). It is the purpose of this contribution to revisit the development of the UML module concept, to criticize its current form, and to present a compact and precise definition of its visibility rules. The integration of still missing concepts of component-based architecture description languages is out of the scope of this contribution. It is one of the main tasks of the OMG task force which is responsible for the development of a real-time modeling extension of UML.