scope:

The purpose of recommending the Specification and Description Language is to provide a language for unambiguous specification and description of the behaviour of telecommunication systems. The specifications and descriptions using the language are intended to be formal in the sense that it is possible to analyse and interpret them unambiguously.

The terms specification and description are used with the following meaning:

a) a specification of a system is the description of its required behaviour; and

b) a description of a system is the description of its actual behaviour (that is, its implementation).

A system specification, in a broad sense, is the specification of both the behaviour and a set of general parameters of the system. However, the Specification and Description Language is intended to specify the behavioural aspects of a system; the general parameters describing properties like capacity and weight have to be described using different techniques.

This Recommendation gives an overview of the series of Recommendations that define SDL-2010, defines terms, conventions including meta-languages, tool compliance and the basis of data for SDL-2010.

NOTE - Since there is no distinction between use for specification and its use for description, the term specification is used in the SDL-2010 Recommendations for both required behaviour and actual behaviour.

Objective

The general objectives when defining the Specification and Description Language have been to provide a language that:

a) is easy to learn, use and interpret;

b) provides unambiguous specification for ordering, tendering and design, while also allowing some issues to be left open;

c) is able to be extended to cover new developments;

d) is able to support several methodologies of system specification and design.

Application

The Recommendations for SDL-2010 provide the reference manual for the Specification and Description Language. This Recommendation provides an overview of the language and the conventions used to define the language. A methodology framework document, which gives examples of Specification and Description Language usage, is available as the Supplement to the Recommendation ITU-T Z.100 series originally produced in the study period 1992-1996.

The main area of application for the language is the specification of the behaviour of aspects of real-time systems, and the design of such systems. Applications in the field of telecommunications include:

a) call and connection processing (for example, call handling, telephony signalling, metering) in switching systems;

b) maintenance and fault treatment (for example, alarms, automatic fault clearance, routine tests) in general telecommunication systems;

c) system control (for example, overload control, modification and extension procedures);

d) operation and maintenance functions, network management;

e) data communication protocols;

f) telecommunication services.

The Specification and Description Language is, of course, usable for the functional specification of the behaviour of any object whose behaviour is specifiable using a discrete model; that is, where the object communicates with its environment by discrete messages.

The Specification and Description Language is a rich language and is usable for both high level informal (and/or formally incomplete) specifications, semi-formal and detailed specifications. The user chooses the appropriate parts of the Specification and Description Language for the intended level of communication and the environment in which the language is being used. Depending on the environment in which a specification is used, it is possible many aspects are left to the common understanding between the provider and the user of the specification.

Thus the language is used for producing:

a) facility requirements;

b) system specifications;

c) ITU-T Recommendations, or other similar standards (international, regional or national);

d) system design specifications;

e) detailed specifications;

f) system design descriptions (both high level and detailed enough to directly produce implementations);

g) system testing descriptions (in particular in combination with Message Sequence Chart [MSC] and Testing and Test Control Notation [TTCN]).

The user organization is able to choose the appropriate level of application of SDL-2010.

System specification

A specification using the Specification and Description Language defines system behaviour in a stimulus/response fashion, assuming that both stimuli and responses are discrete and carry information. In particular, a system specification is seen as the sequence of responses to any given sequence of stimuli.

The system specification model is based on the concept of communicating extended finite state machines.

The Specification and Description Language also provides structuring concepts that facilitate the specification of large and/or complex systems. These constructs allow the partitioning of the system specification into manageable units that are capable of being handled and understood independently. It is possible to perform partitioning in a number of steps resulting in a hierarchical structure of units defining the system at different levels.