In practice most architectural descriptions are informal documents. They are usually centered on box-and-line diagrams, with explanatory prose. Visual conventions are idiosyncratic, and usually project specific. As a result, architectural descriptions are only vaguely understood by developers, they cannot be analyzed for consistency or completeness, they are only hypothetically related to implementations, their properties cannot be enforced as a system evolves, and they cannot be supported by tools to help software architects with their tasks.

There exist several architecture description languages, but we are interested in the use of UML. We aim to identify requirements on architectural modeling and how different modeling concepts of UML meet these requirements. This paper is not intended as a critique of the UML but as a discussion of approaches to modeling architectures that have been tried, more or less successfully.