  UML activity diagrams have become an established notation to model control
and data ow on various levels of abstraction, ranging from fine-grained
descriptions of algorithms to high-level workflow models in business
applications. A formal semantics has to capture the flexibility of the
interpretation of activity diagrams in real systems, which makes it
inappropriate to define a fixed formal semantics. In this paper, we define a
semantics with semantic variation points that allow for a customizable,
application-specific interpretation of activity diagrams. We examine concrete
variants of the activity diagram semantics which may also entail variants of
the syntax re ecting the intended use at hand.
