Annex 1
		5.8.2.3 Specification and Description Language (SDL), (SBM Part)

  Specification and Description Language (SDL)

Contents		1 Identification/Definition of the Method 2 Brief Characteristic of the Method 3 Appraisal of the Method 4 Application of the Method in the V-Model 5 Interfaces 6 Further Information 7 Literature

1 Identification/Definition of the Method

2 Brief Characteristic of the Method

3 Appraisal of the Method

Criteria for the Application of SDL:

• SDL is specially suited for the behavior modeling of (sub-) systems with relative few but complex components. The time sequence diagrams (though not part of the SDL standard but designed for the cooperation with SDL) are particularly applicable for the specification of the system behavior as seen from the user's point of view; based on its simple form they are also easy to handle.

Strong Points of SDL:

• The strong points of SDL are the simple dynamic semantics ("SDL machine") properly modeling the behavior of real-time systems. This also includes the possibility to dynamically generate process instantiations. The method has already been applied for many years to specify complex telecommunication systems.

  The special value of the method is based on the combination of behavior specification and system structuring without a method break; the asynchronous communication mechanisms as an overall basis are valuable for later implementation.

  Based on the simple dynamic semantics and the direct transmission of signals important dynamic characteristics of a specified system (e. g. deadlocks, race conditions, reachability, etc.) are comprehensible.

Peculiarities to be taken into consideration when modeling with SDL:

• A possible loss of signal effects may be a disadvantage in the application for the behavior modeling. This can be the result of the semantics when handling the process input queue (see /SDL, 1985a/, p. 101, chap. 2.3.5, /SDL, 1985b/, Annex D, chap. D.4.3.4.2.1, p. 109). Handling the process input queues may be controlled by applying the save mechanism, though (see /SDL, 1985a/, p. 101, chap. 3.3.2, /SDL, 1991/ chap. 3.8.1, chap. 8.3.4) so each state only consumes the signals required for its activation and leaves other signals in the queue. This has the effect as if each state has its own signal input queue which predominantly corresponds to the semantic intuitively expected.

Method Familiarization

• Based on the total functionality range of the method and because of a number of special symbols, the notation is relatively comprehensive. Basic components are easy to learn, though. The adjustment of process and block tree diagrams requires special attention. The dynamic semantics are of moderate size and free of problematic assumptions; they contain the rules required for the execution of parallel, asynchronous communicating automata and for solving realistic, possible conflicts. Training (see /SDL, 1985c/) and experience are needed for this method.

Tool Support

• Tool support is required for the generation and reconstruction of the specification of systems with considerable size (for more information see /SDL, 1985b/, Annex D, chap. D.10). So far, several tools supporting this method are available on the market.

4 Application of the Method in the V-Model

5 Interfaces

The formal SDL definition renders the language suitable for the mapping on programming languages (see /SDL, 1985b/, Annex D, chap.D.10.2, D.10.8).

6 Further Information

7 Literature

GDPA Online Last Updated 01.Jan.2002 Updated by Webmaster Last Revised 01.Jan.2002 Revised by Webmaster