The formal semantics of SDL-2000: Status and perspectives

In November 1999, the current version of specification and description language (SDL), commonly referred to as SDL-2000, passed through ITU-T. In November 2000, the formal semantics of SDL- 2000 was officially approved to become part of the SDL language definition. It covers both the static and the dynamic semantics, and is based on the formalism of abstract state machines (ASMs). To support executability, the formal semantics defines, for each SDL specification, reference ASM code, which enables an SDL-to-ASM-compiler.In this paper, we briefly survey and compare existing approaches to define the semantics of SDL formally. The ITU-T approach is then outlined in more detail, addressing the following steps: (1) mapping of non-basic language constructs to the core language, (2) checking of static semantics conditions, (3) definition of the SDL abstract machine (SAM), and (4) definition of the SDL virtual machine (SVM). The paper concludes with experiences from the SDL-to-ASM-compiler project. It is proposed that the SDL-2000 semantics can be adapted and extended to formally define the meaning of UML 2.0 class, composite structure, and statechart diagrams.