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Specification and Design Language.

Defined by the ITU-T (recommendation Z100) to provide a tool for unambiguous specification and description of the behaviour of telecommunications systems. The area of application also includes process control and real-time applications. SDL provides a Graphic Representation (SDL/GR) and a textual Phrase Representation (SDL/PR), which are equivalent representations of the same semantics. A system is specified as a set of interconnected abstract machines which are extensions of the Finite State Machine (FSM).

1. System Software Development Language. System software for the B1700. "System Software Development Language Reference Manual", 1081346, Burroughs Corp (Dec 1974).

2. Specification and Description Language. ITU-T. Specification language with both graphical and character-based syntaxes for defining interacting extended finite state machines. Used to specify discrete interactive systems such as industrial process control, traffic control, and telecommunication systems. Proc Plenary Assembly, Melbourne 14-1988-11-25, Fasc X.1, CCITT. "Telecommunications Systems Engineering Using SDL", R. Saracco et al, N-H 1989. Available from Verilog, MD. (See XDL).

3. Shared Dataspace Language. "A Shared Dataspace Language Supporting Large-Scale Concurrency", G. Roman et al, Proc 8th Intl Conf Distrib Comp Sys, IEEE 1988, pp.265-272.

4. Structure Definition Language. Used internally by DEC to define and generate the symbols used for VAX/VMS internal data structures in various languages.

5. System Description Language. language used by the Eiffel/S implementation of Eiffel to assemble clusters into a system. (see Lace).


(Specification and Description Language) A modeling language used to describe real-time systems. It is widely used to model state machines in the telecommunications, aviation, automotive and medical industries. SDL is used to model the details of a system, which can be simulated and proven, whereas UML is used to model at a higher level of abstraction.

There are three parts to an SDL diagram: the system definition, block and process. The system definition defines the major nodes (blocks) of the system such as clients and servers, while the block charts show more details. The process diagram shows the processing steps in each block. See state machine and UML.

SDL Process Diagram
This simple system in a server lets the user add two numbers at a terminal. There is more detail in this diagram than in the UML model from which it originated (see below). (Diagram courtesy of Telelogic, AB,

UML Equivalent
This UML diagram was turned into the SDL description above by Telelogic's UML to SDL Translator (see UML for more diagrams). (Diagram courtesy of Telelogic, AB,
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