Re: SDL-News: Plans for the SDL Forum?

Subject: Re: SDL-News: Plans for the SDL Forum?
From: Rick Reed TSE (
Date: Mon Jan 05 2004 - 13:55:15 GMT

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Dear All,

William has asked for some information on plans for SDL.

As both Chairman or the SDL Forum and also the rapporteur for the ITU
standardisation work on SDL (from September 2003), I am the correct person
to answer.

William H. Skelton at wrote on 12/17/03 23:13:

> Writing from the SDL Task Force ( to stay
> synchronized, I would like to ask what activities are taking place in the
> SDL Forum regarding standardization, amendments to the language, future of
> SDL? Is SDL-2000 the end of the road? Does anyone support it?
> A few words from the Chairman, or the board, would be helpful outlining
> their plans for promoting SDL and cooperating with tool suppliers. Where
> do we see the greatest opportunities and challenges? What is happening on
> the UML front?

SDL-2000 is not the "end of the road", but certainly there is no great
pressure for change at the current time.

The history for SDL is that there has been a major update approximately
every 8 years, with stability and only some minor changes in between. 2004
is one of these "in between" times.

Based on previous experience there was an initial objective for SDL-2000 to
aim for implementation BEFORE standardisation to minimise the difference
between the standard and tools. In part this was achieved, because most of
the new SDL-2000 features were implemented by at least one tool.
Unfortunately different tools tackled different features and there is still
no tool that implements almost all of the features - though in reality
Cinderella and SDT come pretty close.

In retrospect, one thing that was a mistake in the SDL-2000 work was to
"clean up some of the textual syntax" - in particular for procedure and
operator headings. It must be said that two of the major advocates for the
change were Telelogic and Verilog. The justification was that the SDL syntax
did not look like the programming languages most users were familiar with.
What happened in reality was that the old syntax - although idiosyncratic -
worked and there was insufficient advantage to users/tool-vendors for a
change (especially those with legacy models). The latest release of SDL-2000
has fixed the situation by allowing both the old and new syntax.
The old syntax is in an Annex with therefore an implied lower status.

Another change that has been adopted recently has been to define compliance.
SDT and Cinderella (I swapped the order this time - to be even-handed)
are compliant.

SDL-2000 was a large project and not everything that was considered made it
into the final cut. For example, there was a lot of discussion about
bringing interfaces and signals into line with data types so that:
a) a signal signature could also be treated as a STRUCT definition;
b) the need to store signal parameters in local variables could be avoided;
... plus other advantages.

There are a large number of items of "unfinished business" of this type,
many of which are captured in a "to do" list, which still needs to be done.
As rapporteur, making sure this and other outstanding issues at least get
considered and the decisions documented.

After SDL-2000, several of the SDL experts focussed effort on UML 2.0.
This was not without the consent of ITU-T, because it was already recognised
this would (probably) be the future. SDL-2000 itself and the Z.109
Recommendation were already part of the way towards UML/SDL integration.

Of course, SDL is rooted in the telecommunications industry, and we all know
that most players have suffered significant financial set backs in the last
few years. The result for SDL has been a cut back in the amount of resources
in developing both the language and tools: it is no secret that Telelogic
has had to downsize, for example, and other standards participants such as
Siemens, Nortel, Ericsson, Motorola have also had less resources for this
work. However, lets be positive and assume an industry upturn in 2004 and a
consequent increase in resource. In that case what is in store?

Current ITU plans are focused on the following:

1) Defining encoding rules for SDL;

2) Further integration of UML/SDL with a revised Z.109 based on work to be
carried out by ETSI STF250, and probably with some consequent updates to
Z.100 for UML/SDL alignment.

3) Further restructuring of the SDL Recommendations. What has been agreed in
principle is to separate features that depend on modelling from features
that map directly onto the abstract syntax. Personally I would also like to
see a clearly identified subset of the language as well - but that is not

Items for discussion at ITU-T are:

1. The need for and extent of changes to the SDL language itself during the
next four years;

2. The support provided by the ITU staff for SDL including (but not limited
to) checking SDL in other Recommendations for compliance with the standard;

3. The ITU promotion of SDL and the other ITU-T languages;

4. If and how the ITU-T should identify a clearly defined subset of SDL.

It is in the current constitution of the the SDL Forum Society that its work
has to be aligned with that of ITU-T. The future as I see it, is that the
Society members can take a more active role in preparing and building
consensus on standards prior to publication by ITU-T. In some ways this
could be similar to the production of SDL-2000 where the experts met
approximately every 3 months at "joint SDL Forum and ITU-T" meetings. The
purpose and a major advantage of organising these meetings in this way the
easy participation of non-ITU members in the work. These days there is no
longer a need for such frequent physical meetings, because much work can be
done by email correspondence and internet file sharing - though for decision
making on contentious issues I think the occasional physical meeting is
still needed. These meetings can be integrated into other events such as the
SDL Forum/SAM workshops.

There seems to be no good reason for publishing updates of the SDL standard
itself outside the ITU-T. An ITU Recommendation has international status
recognised by nation states because of the set up of ITU as part of the
United Nations. The ITU has the infrastructure for establishing and
maintaining these publications over a number of years, and can be remarkably
quick (often quicker than ad hoc "standards" bodies) in updating the
documents. The criticisms of the ITU-T (such as time between approval and
publication, cost and accessibility of publications) are well known by ITU-T
and are being addressed. For example, the publications are now available via
the WWW and the "pre-published" text is available within a couple of weeks
from approval. The delay in final publication is often due to waiting for
aligned translations in all three official languages (French, English,
Spanish) but the approval group can agree to publish in one language only
thus avoiding this delay. I expect ITU-T to become even faster in getting
results out in the future, and possibly making WWW access even easier.

As indicated on the translation issue, it is the technical study group that
makes some of the decisions that impact on what is available. As far as SDL
is concerned the decisions made by this group over the last 12 years have
resulted in a decrease in user documentation supported by ITU-T. Prior to
1992 the SDL Recommendations were supplemented by 180 pages of "User
Guidelines" (ISBN 92-61-03751-8) and a training course, but when the
language was updated for SDL-92 no-one could be found to update this
document with the result it was decided it was better to delete it and
replace it with "Methodology Guidelines" (still available). While the
methodology document provided some advice on application of SDL, it did not
include a description of the language feature by feature as in the "User
Guidelines". For such a description the user either had to reply on
understanding the Z.100 Recommendation or published papers and books. It was
the decision of the technical group that such material was better published
outside ITU-T and training could be provided externally.

When SDL-2000 was published, the original intention was to update the
Methodology Guidelines, but again resource constraints meant that this was
not done, but this time it was decided to retain the old document even
though it was slightly out of date. The changes in SDL-2000 meant that all
the examples in the earlier version of Z.100 needed to be checked for both
correctness and suitability. As the deadline for approval at the end of 1999
approached and this work had not been completed, it was decided that it was
easier to remove examples rather than update them - partly on the principle
that the examples should not add anything the actual language definition.
However, the result was that Z.100 for SDL-2000 is more difficult to

Part of the ITU-T discussion on what to publish also involved the SDL Forum
Society, because it was agreed that some of the methodology material, user
guidelines explaining SDL and tutorial material were more appropriate for
the Society to publish. The rationale is that the ITU-T publications are
Standards and ITU-T resources should be focussed on the publication and
maintenance of the standard itself. The role of the Society was initially
just publicity and dissemination, and further development of the languages
was a change to the constitution.

The situation today is that the Society could (and maybe SHOULD) take on the
role of producing more documentation for users. Views are therefore welcome
on this issue (in particular from Members - please email the members list).

The current promotion effort of the Society is therefore limited to:

1. Running the SAM workshop (this year in Ottawa - see and SDL Forum (next year);

2. Recognition of a workshop at ISSRE04 on SDL related issues and will
assist with publicity - University of Göttingen (Prof. Dr. Dieter Hogrefe)
is providing support for this event.
NOTE: However, I am assisting and I need to do some work on this - "watch
this space".

3. Continuing to support the WWW site.

As usual, we are liasing with tool suppliers on the workshop.
Suggestions of further collaboration with tool suppliers to promote SDL are
welcome, especially I do not have any specific ideas myself.
Are there any other suggestions on promotion (in particular from Members -
please email the members list)?

Finally, this report would not be complete without stating that the Society
is providing some funding towards my participation in the next ITU-T meeting
in March 2004.

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

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