![]() |
![]() |
![]() |
![]() |
![]() |
General about the SDL Language
SDL (Specification and Description Language) is a standard language for specifying and describing systems1. It has been developed and standardized by ITU-T in the recommendation Z.100.
The development of SDL started in 1972 after a period of research work. The first version of the language was issued in 1976 and it has been followed by new versions every fourth year. The latest versions expanded the language considerably, and today SDL is a "complete" language in all senses.
In the SDL Suite, there is full support of SDL including some of the SDL-96 concepts. For more information about the SDL support in the SDL Suite, see Compatibility with ITU SDL.
Modularity
An SDL specification/design (a system) consists of a number of interconnected modules (blocks). A block can recursively be divided into more blocks forming a hierarchy of blocks. The channels define the communication paths through which the blocks communicate with each other or with the environment. Each channel usually contains an unbounded FIFO queue that contain the signals that are transported on the channel. The behavior of the leaf blocks is described by one or more communicating processes. The processes are described by extended finite state machines.
Object Oriented Design
SDL furthermore supports object-oriented design by a type2 concept that allows specialization and inheritance to be used for most of the SDL concepts, like blocks, processes, data types, etc. The obvious advantage is the possibility to design compact systems and to reuse components which in turn reduces the required effort to maintain a system.
Graphical and Textual Notations
SDL gives a choice of two equivalent syntactic forms; a Graphical Representation (SDL/GR) and a textual Phrasal Representation (SDL/PR). The SDL Suite supports both notations.
Application Areas
Currently, SDL is mainly known within the telecommunication industry, but it also has broader areas of application and is now gaining acceptance within the real-time software industry. The application areas may be summarized as follows:
1
- Type of system described by SDL: Real-time, interactive, distributed.
- Type of information provided by SDL: Behavior and structure.
- Level of abstraction supported by SDL: From system overview to functional detail.
No distinction is made in SDL between the terms "specification" and "description", although they generally have different meanings in SDL applications.
2SDL has adopted the term type which corresponds to the term class used in many of the OO notations and programming languages.
http://www.ibm.com/rational |
![]() |
![]() |
![]() |
![]() |