Describing Computer Languages

Concept Definitions First we present the abstract construct definitions that were used for the SDL2000 meta-model. There are different levels of abstractions. Some constructs are so general that they are used in virtually every object-oriented language, others are more specific and may only be reused among related languages or only within one language. Figure 3.9 shows the abstract structure constructs used by most objectoriented languages. A detailed explanation and documented development of that model can be found in [64]. These constructs are not only relevant to SDL, they are also used in the meta-models of UML and the meta-meta-model of MOF. But even more abstract constructs could be obtained from SDL’s notation itself. Even if they may turn out to be more specific, perhaps distinctive to SDL, they still allow a more compact and therefore easier to understand and easier to use meta-model. Figure 3.10 presents the additional abstract constructs that could be identified in the SDL-2000 notation. A few concrete meta-model classes, those that are marked grey, are shown too. A few remarks: • Many SDL constructs reference a body of some sort. Procedures for example must contain a state automaton defining their behaviour. This state automaton is referred to as a body. The same is true for process typed Agents or the bodies in Composite-state types. To respect the varying nature of bodies, they are modelled to be the most abstract construct: ModelElement. 80 3 Representation – Describing Textual Notations