Formal semantics of interactions in sequence diagrams for embedded software

Recently, sequence diagrams have been extended with the introduction of a set of operators in the latest specification of the Unified Modeling Language 2 (UML 2). Embedded in combined fragments, these operators are intended to simplify the diagram's structure or alter the order of its events. However, the latest specification introduces a non-trivial degree of ambiguity in the interpretation and understanding of sequence diagrams. As these diagrams are increasingly adopted as modeling tools in embedded software, their ambiguity can exacerbate the challenges encountered in embedded system design. To address this ambiguity, this paper presents a formal model in operational semantics based on Abstract State Machines (ASM) to define the semantics of the loop, break and strict operators in sequence diagrams. Specifically, update rules are devised for ASMs to handle important behaviors present in most embedded software operating in distributed or parallel environments. This formal model can be readily extended to define the semantics of the remaining operators including information about time intervals and their related constraints.