1.1 History

Tutorial on SDL-88
Belina, Hogrefe (edits Reed)

The Specification and Description Language is a language for the specification and description of systems that has been developed and standardized by ITU-T, the Telecommunication standards sector of the International Telecommunication Union (ITU). The ITU-T part of ITU was previously known as CCITT (International Telegraph and Telephone Consultative Committee).

Note: No distinction is made in the Specification and Description Language between the terms specification and description, although they generally have different meanings when using the language in applications. The same holds for this tutorial, but for brevity it is called simply a specification language.

The development of the Specification and Description Language started in 1972 after a period of investigations. The first version of the language was issued 1976, followed by new versions in 1980, 1984 and 1988. The 1984 and 1988 versions contained a considerable expansion of the language, which was considered to have reached such maturity that further development was not of interest until SDL-92. The SDL-92 version is more object-oriented with TYPE definitions (similar to UML classes) that than can be used for process instances and data instances (for example). However, these TYPE constructs are actually templates that map onto SDL-88 constructs, so that SDL-92 can always be flattened to SDL-88 and SDL-88 is a subset of SDL-92. In SDL-2000 the TYPE features were made into fundamental components of the language, but from a user viewpoint with the same semantics as SDL-92. Therefore (with a few exceptions) SDL-88 can still be used with tools that support SDL-92 and/or SDL-2000.

SDL-88, was approved 1987 and is defined in [1].

Early versions of SDL had been in use for a long time before 1988. The experience from this use has contributed to improvement of the language. A survey at 2nd and 3rd SDL Forums in 1985 [2] and 1987 [3] showed that SDL was used by about 5000 people around the world. SDL was - of course - also used by the CCITT (now ITU-T) Study Groups in their Recommendations. The Forums showed that the contemporary activities for SDL focused on development of computer based tools for SDL-88. Subsequently there was introduction of this version at administrations and industrial enterprises on a larger scale. In 1990, there were already SDL tools available on a commercial basis to everybody.