Abstract. We define the dynamic semantics of UML State Machines which integrate statecharts with the UML object model. The use of ASMs allows us (a) to rigorously model the event driven run to completion scheme, including the sequential execution of entry/exit actions (along the structure of state nesting) and the concurrent execution of internal activities; (b) to formalize the object interaction, by combining control and data flow features in a seamless way; and (c) to provide a precise but nevertheless provably most general computational meaning to the UML terms of atomic and durative actions/activities. We borrow some features from the rigorous description of UML Activity Diagrams by ASMs in [7].

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Abstract. In UML 2.0 sequence diagrams have been considerably extended, influenced by Live Sequence Charts (LSCs), a very expressive extension of Message Sequence Charts (MSC) with liveness. Nonetheless, fundamental liveness properties can still not be expressed in the new sequence diagrams. In recent work, we have proposed to solve this by enriching sequence diagrams with a simple but powerful Object Constraint Language (OCL) template for liveness. In this paper, we show how to formalize our liveness-enriched sequence diagrams using Abstract State Machines. Sequence diagrams still have several open problems. For example, the semantics of some of the newly introduced operators is ambiguous, and it is not clear how they can be used or combined with other operators. We address some of these issues in the paper. Finally, a further advantage of using ASMs as a semantic model concerns synthesis. It is our ultimate goal to be able to synthesise automatically a state-based object system from our richer sequence diagrams. ASMs are a state-based and operational formalism which therefore eases this task considerably.

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