Various Semantic Interpretations

UML 2.0 specification specifies not only the graphical representation of the state machines, but also their semantics,

however,

already the specification itself contains multiple variation points, where a UML compliant implementations can differ from each other. For example: how to deal with non-determinism, how to deal with unsolicited event in case of protocol state machines, etc.

Add to that, there is not just UML 2.0 around, the UML state machines are quite often referred to as "Harel Statecharts", however, this term is quite ambiguous, because of:

• D. Harel and H. Kugler, The Rhapsody Semantics of Statecharts (or, On the Executable Core of the UML), Integration of Software Specification Techniques for Applications in Engineering, (H. Ehrig et al., eds.), Lecture Notes in Computer Science, Vol. 3147, Springer-Verlag, 2004, pp. 325-354. [download]
• D. Harel and M. Politi, Modeling Reactive Systems with Statecharts: The STATEMATE Approach, McGraw-Hill (258 pp.), 1998 [download]

(Will be explained ...)