SDL-News: Fwd: Re: [SDLTF-Members] Summary of SAVE Issues Discussed

Subject: SDL-News: Fwd: Re: [SDLTF-Members] Summary of SAVE Issues Discussed
From: William H. Skelton (
Date: Thu Dec 04 2003 - 22:22:37 GMT

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-----From "William H. Skelton" <> to sdlnews -----

Dear Rick,

Thank you for your comments, which correct my hurried inaccuracies in detail.

The big picture still remains valid in my opinion and the length of
explanation needed to counter what I have expressed in a couple of
sentences surely indicates the complexity of what apparently is being
defended as simple.

I repeat, save is not in the subset for the reason that is not essential!

It is not a question of how nice the feature is or how useful it is or how
it works even; only if there is a 'need' for it that cannot be fulfilled by
a simple mechanism already in the subset, such as SEQUENCE OF.

It would be nice if we could keep these issues separate. :-)

More comments below...


>Date: Thu, 04 Dec 2003 21:45:27 +0000
>Subject: Re: [SDLTF-Members] Summary of SAVE Issues Discussed
>From: Rick Reed TSE <>
>To: <>
>CC: SDLnews <>
>William H. Skelton at wrote on 04/12/2003 18:31:
> > 1.2) There has been confusion about how the save construct works and why it
> > is useful (execution model is not transparent, inter-state dependencies are
> > created). Apart from state reduction, there have been no applications
> > presented where it is needed (William).
>I would be surprised if anyone that has used SDL tools such as Cinderella,
>GEODE or SDT to any extent is confused about the way that SAVE works.

But there has been confusion and also a large number of emails and
paragraphs of detail explaining it. Furthermore part of the problem lies
in looking at the effect on other features.

>I do not agree with the analysis that "Apart from state reduction, there
>have been no applications presented where it is needed". It seems to me that
>several examples were given, and Philipp gave an example that is difficult
>to put into SDL without SAVE, because there is a state explosion otherwise.

State explosion is what state reduction is trying to avoid, right? :-)

No examples were given where it is needed; all examples for buffering data
could be handled with SEQUENCE OF and you showed that Philipp's example
could be done a different way yourself!

> > 1.4) Spontaneous transitions are not in the subset; are they needed
> (Philipp)?
>If the subset is to enable test stubs to be written, then I would think they
>would be needed.

As someone not familiar with this subject it would useful to understand
what test stubs are and why spontaneous transitions help. It may have a
bearing on the issues related to test requirements.

> > 2.1) There are no operators in pre SDL-2000 that allow SEQUENCE OF to be
> > manipulated(!!!)
>This is an incorrect statement.
>The operators were defined when it was allowed to use ASN.1 data with SDL -
>standardised by Z.105 March 1995.
>These operators are supported by SDL tools.

To save time, it would help if you could list these for us, as previous
emails had lead to this conclusion. From Alki's comments we need add to
back, remove from front, clear, possibly more, but I have not seen an
answer how this is supported already.

> > and SDL-2000 strings and operators are not in the SDL
> > subset.
>Strings are not an SDL-2000 feature. They existed in SDL-92, SDL-88 and

Your example to the task force was a more complex use of strings, that
looked to me like strings of data-types with generic operators for working
on them. But I have to admit I only scanned those comments quickly; have I
missed the point?

>I was under the impression that the supported data types and operations were
>under discussion.

We have identified in the first task force discussions that the ASN.1 data
types, in principle according to X.680, are the minimum requirement. The
mechanisms you presented for implementing queues seemed to use much more
advanced features, which lead others to comment on their complexity
compared to what was under discussion.

The main point here is the use of literals, operators(!) and a double-check
if anything is missing.

> > An analysis of how to use SDL-2000 operators on SEQUENCE OF, which
> > is a valid SDL/ASN.1 type in the subset, is pending (Alkis).
>Is there a good reason to deviate from ITU-T SDL?

That is what we are trying to find out! :-)

And so far I think the progress is surprisingly good, not least due to your
help in clarifying some of the opaque issues!

>Rick Reed -
>Tel:+44 15394 88462 Mob.:+44 7970 50 96 50

William H. Skelton, Engineering Dept.
SOLINET GmbH Solutions for Innovative Networks
Mittlerer Pfad 26, 70499 Stuttgart, Germany
Tel +49 711 1398 1377, Fax +49 711 866 1240
Mobile +49 171 247 6688,

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