specification and description language (SDL)

The Specification and Description Language (SDL) is a specification and description language of the International Telecommunication Union( ITU) with which the behavior of switching systems and their development are supported. The SDL description language dates from the 1970s and was standardized by the ITU under standards Z.100ff.

The Specification and Description Language is used to describe functions, protocols and services within and between exchanges and terminal equipment. The description language is based on graphic elements with which real-time systems are described. There are graphical elements for the description of the architecture and others for the description of the behavior. The use of the graphic symbols and their sequence are specified by rules. There are two syntactical characteristics, that are the Graphical Representation (SDL/ GR) and the Phrase Representation (SDL/ PR). These are different forms of representation of the common semantics. SDL was constantly developed further and included among other things in OSDL the object-oriented programming and the abstract syntaxASN.1.

With the SDL description language the hierarchical system structure can be described, likewise the system conditions and the sequential control. The system structure of the SDL language consists of blocks, in which processes run. The blocks are interconnected and exchange information with each other through the connection. The running processes are independent of each other and can run simultaneously.