UML as an Architecture Description Language

Architecture Description Languages (ADLs) are specialized formal languages supporting modeling and reasoning on software architectures. Although number of ADLs counts in the tens, their popularity and usage by practitioners is very low. The object- oriented Unified Modeling Language (UML), which has become the OMG standard, offers a great variety of concepts for the definition of the structure and the expected behavior of a software system. Unified Modeling Language is de facto industrial standard, however not fully qualified ADL. It has the potential to replace many previously used software architecture description language. Compared with other ADLs, UML has the main drawback that its module concept is continuously changing from version to version without reaching a well-defined state. 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.