Formalize UML 2 Sequence Diagrams

UML 1 sequence diagrams have been widely employed for modeling software requirements and design. UML 2 introduced many new features, such as Combined Fragments, to make sequence diagrams more expressive than UML 1. However, the lack of formal semantics descriptions of these features makes it difficult for practitioners and tool builders to construct and analyze sequence diagrams that specify high assurance systems. In previous work, we presented a formalism, template semantics, for describing the operational semantics of behavioral notations. In this paper, we adapt template semantics to describe the combined fragments and other constructs of sequence diagrams. We believe that formalizing the semantics of sequence diagrams is an important step towards synthesizing multiple sequence diagrams into behavioral models (i.e., state machines) and formally analyzing them.