Interpretation of a system description means the creation, initiation and subsequent running of a system instance. This is performed by an imaginary SDL machine, similarly to running a target program by a computer. To make this analogy complete, a system instance should also contain e.g. signal descriptions, but it is probably simpler to assume that the SDL machine refers to the system description whenever it needs further information. It is this machine that e.g. creates a process when interpreting a create request, creates and assigns a unique address to it, and keeps record of all created process addresses within the system and its environment. The dynamic semantics part of the formal definition of SDL describes in- detail the behaviour of this SDL machine.

Before a system instance can be created, a number of transformations and selections must be made to the original concrete system description, written by the user of SDL in one of the two concrete representation forms: SDL/GR and SDL/PR (or in a combination of these), see figure 36. First, all the shorthands are transformed in a predefined order. Then the concrete syntax is transformed into a simpler, internal, abstract syntax. The resulting abstract system description still contains optional parts, since a block description can contain both process descriptions and subblock descriptions. Then a consistent partitioning subset is selected (containing no optional parts), which is then interpreted.

The transformation of the original concrete system description to a consistent partitioning subset is described in detail in the static semantics part of the formal definition of SDL. This procedure is the means to check the correctness and to establish the semantics of the original concrete system description. It is generally performed by an analyzer tool.

Figre36 Overview SDL concepts

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