Re: SDL-News: SDL and its usage

Subject: Re: SDL-News: SDL and its usage
From: Rick Reed TSE (
Date: Sat Jun 23 2001 - 16:49:27 GMT

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Elangovan Angannan at wrote on 23/06/2001 15:04:

> Is there any use of SDL, if I am not using it for Code
> Generation? What I feel is, when SDL is not used to
> produce C/C++ code, then normal state diagram with
> some SDL agent representation (like system) is enough,
> Implementation is not necessary.

Dear All,

Yes, of course there is.

SDL can be used to specify a system that is implemented in some other way.
In fact this was the original intention of SDL where it was used to specify
protocols in telecoms systems which were implemented in hardware and
programmes written in assembly language.

Though the world has changed, this is still a valid use of the language and
it is used for standardised protocols and for test case derivation.

SDL models can be used for "proof of concept" or to design logical behaviour
before going into implementation detail.

In many cases, it is not even necessary to simulate the SDL model to find
logical inconsistencies during design: the readability of (graphical) SDL is
one of its key attributes. You can make an SDL model to help you understand
and reason about a design: either for individual use, or for discussion and
review with others. For these purposes it is not necessary to make every
task formal enough to be converted to C/C++: an adequate informal
description is enough.

Once a model has become elaborate, the more subtle design flaws are only
likely to be found by tool analysis, simulation or execution. However, for
simulation there may still be some parts that are informal, and in this case
a machine simulator has to ask for human input during simulation.

I am not sure what is meant by a "normal state diagram". If this means some
notation other than SDL, the key issue is that SDL is Standardised so there
should be no doubt about what the specified behaviour is. SDL was made a
standard to give state diagrams a precise, well-defined meaning.

However, if Elangovan is saying there is a use for SDL even it is not used
to directly generate code, I thoroughly agree.

Rick Reed -
Tel:+44 1455 55 96 55 Fax:+44 1455 55 96 58 Mob.:+44 7970 50 96 50

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