UML 2.0 Sequence Diagrams' Semantics

Scenario languages are widely used in software development. Typical usage scenarios, forbidden behaviors, test cases and many more aspects can be depicted with graphical scenarios. Scenario languages were introduced into the Unified Modeling Language (UML) under the name of Sequence Diagrams. The 2.0 version of UML changed Sequence Diagrams significantly, the expressiveness of the language was highly increased. However, it was carried out without defining a precise semantics for the language. This paper presents the semantics defined in the specification, collects and categorizes the problems with the current approach, and gives a survey of proposed formal semantics for Sequence Diagrams.