SDL-News: Summary of SAVE Issues Discussed

Subject: SDL-News: Summary of SAVE Issues Discussed
From: William H. Skelton (
Date: Thu Dec 04 2003 - 18:31:16 GMT

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Dear Task Force Members,
CC: SDL News (Interested person not on the task force list can register at

Here is a brief summary of the main points regarding the SAVE construct
discussed in the last few days on the task force email distribution list
and which we intend to close before the draft document version 1.2.

1) There is a genuine need for save based on reducing the states needed to
handle signals that could arrive in an undefined order (Qing Li).

1.1) There is no atomic way to clear saved signals from the input queue;
one suggestion is to use a TRUE continuous signal, which is not in the
subset (Rick).

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).

1.3) There may be a link to the snapshot semantics of TTCN (Qing).

1.4) Spontaneous transitions are not in the subset; are they needed (Philipp)?

2) For the buffering of data, there is an alternative of using a queue,
which can be simply implemented using SEQUENCE OF and complies with
conventional views on software engineering (Alkis).

2.1) There are no operators in pre SDL-2000 that allow SEQUENCE OF to be
manipulated(!!!) and SDL-2000 strings and operators are not in the SDL
subset. 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).

2.2) A relay mechanism to receive and broadcast a signal has been raised

Many thanks to all involved for their comments and opinions.


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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