摘要：The abstract syntax and static semantics of UML, the widely-used generalpurpose
graphical modeling language, have been standardized in a four-layer metamodeling
framework. However UML's dynamic semantics, such as UML Precise Action Semantics
and the behaviors like activities, interactions and state machines, are only
standardized in a natural language-English. It is commonly argued that such
informal description inevitably involves ambiguities and lacks rigorousness,
precluding the early simulation and reasoning about a UML system design. Here we
select Action Semantics (AS) as the vehicle to formalize UML. AS is a mature
semantics description framework which has advantages of intelligibility,
modularity and practicability. In our approach, we formalize UML indirectly by
formalizing its textual correspondent-an extended Action Language, which plays a
key role as the interface between UML and its action semantics.
