1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 “ TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-%!.3G0G0/(b) that a specification of a system is the description of its required behaviour;(c) that a description of a system is the description of its actual behaviour;(d) that a universal method for specif
2、ication and description should bring economic benefits;(e) that the CCITT has adopted such a method called the Specification and Description Language (SDL) asdescribed in CCITT Recommendations Z.100 to Z.104,recommends(1) the adoption within the ITU of the use of the CCITT Specification and Descript
3、ion Language (SDL) forunambiguous specification and description of telecommunication systems (see Annex A);(2) that the possibilities for application of SDL in areas of common interest for the purposes of standardizationbe brought to the attention of other international bodies (e.g. the IEC and ISO)
4、 for their consideration.ANNEX A(to Recommendation B.17)Introduction to SDLThe purpose of recommending SDL is to provide a language for unambiguous specification and description ofthe behaviour of telecommunications systems. The specifications and descriptions using SDL are intended to be formalin t
5、he sense that it is possible to analyse and interpret them unambiguously.The terms specification and description are used with the following meaning: a specification of a system is the description of its required behaviour, and a description of a system is the description of its actual behaviour.SDL
6、 also provides structuring concepts which allow a system to be partitioned so that it can be defined,developed and understood one part at a time.These concepts are of value both initially in specifying a system, when different aspects can be independentlydealt with, and later in describing a system,
7、 when the description structures should match the system structure._1)A similar text will be submitted to the CCIR as revision of Recommendation 664.2 Fascicle I.3 - Rec. B.17SDL gives a choice of the use of two different forms when representing SDL descriptions; a graphicrepresentation (SDL/GDR) an
8、d a textual phrase representation (SDL/PR). As they are both specific representations ofthe same SDL semantics, they are equivalent from a semantic point of view.ObjectivesThe general objectives when defining SDL have been to provide a language that: is easy to learn, use and interpret in relation t
9、o the needs of an operating organization; provides unambiguous specifications and descriptions for ordering and tendering; may be extended to cover new developments; is able to support several methodologies of system specification and design, without assuming any one ofthese.ScopeThe main are of app
10、lication for SDL is the description of the behaviour of aspects of telecommunicationssystems. Applications include: call processing (e.g. call handling, telephony signalling, metering) in stored programme control (SPC)switching systems; maintenance and fault treatment (e.g. alarms, automatic fault c
11、learance, routine tests) in generaltelecommunications systems; system control (e.g. overload control, modification and extension procedures); data communication protocols.SDL can of course also be used for the description of any behaviour capable of being described using a discretemodel, i.e. communicating with its environment by discrete messages.A description of SDL is given in CCITT Recommendations Z.100 to Z.104.
