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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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In UML 2.0 sequence diagrams have been considerably extended but their expressiveness and semantics remains problematic in several ways. In other work we have shown how sequence diagrams combined with an OCL liveness template gives us a much richer language for inter-object behaviour specification. In this paper, we give a semantics of these enriched diagrams using labelled event structures. Further, we show how sequence diagrams can be embedded into a true-concurrent two-level logic interpreted over labelled event structures. The top level logic, called communication logic, is used to describe inter-object specification, whereas the lower level logic, called home logic, describes intra-object behaviour. An interesting consequence of using this logic relates to how state-based behaviour can be synthesised from inter-object specifications. Plans of extending the Edinburgh Concurrency Workbench in this context are discussed.

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