Formalize UML 2 Sequence Diagrams

UML 2 sequence diagram introduced many new structured control constructs, such as Combined Fragments, to express concurrent message exchanges. These new features makes it more expressive than it in UML 1, however, the lack of formal semantics descriptions makes it difficult for software practitioners and tool builders to construct and analyze sequence diagrams. In this paper, we adapt our previously developed template semantics to formalize the structured control constructs of sequence diagrams.