Re: MSC-News: Problem with instance-oriented - shared in-line expression textual

Subject: Re: MSC-News: Problem with instance-oriented - shared in-line expression textual
From: UK496 Paul Baker (paul#bae231.comm.mot.com)
Date: Mon Oct 05 1998 - 08:21:23 GMT

The originator of this message is responsible for its content.
-----From UK496 Paul Baker <paul#bae231.comm.mot.com> to mscnews -----

Hi Ekkart,

> Dear Paul,
> can you give a simple example? I cannot see immediately your point because
> of the shared construct.
>

If we have two action boxes a and b each of which reside upon different
instances (I, J) within an 'alt' inline expression, it is not possible
to determine whether the expression has the choice of executing:
 
- action a followed by action b, or vice-versa

or

- action a or action b, not both.

Using the above example the instance-oriented grammar would look as
follows:

instance I;
        alt begin i,j;
                action a; /* is this event part of the same choice as action b? */
        alt end;
endinstance I;
instance J;
        alt begin i,j;
                action b; /* is this event part of the same choice as action a? */
        alt end;
end instance J;

I hope this helps.

Kind Regards

Paul. 

-- 

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Ekkart Rudolph wrote:
> 
> The originator of this message is responsible for its content.
> -----From Ekkart Rudolph <rudolphe#informatik.tu-muenchen.de> to mscnews  -----
> 
> Paul Baker wrote:
> 
> > Dear MSC folks,
> >
> > I think there is a problem regarding the instance-oriented textual
> > grammar for the shared
> > inline ‘alt’ and ‘par’ expressions (section 5.3  of Z.120), which:
> >
> >>
> 
> > (2) makes it impossible to define the semantics for alt and par
> > expressions using the
> > instance-oriented grammar. The reason for this is that it is not
> > possible (in some cases)
> > given the information provided to determine which events, existing on
> > different instances,
> > are associated with different alt or par arguments. And in fact
> > whether events are
> > indeed associated with the same alt or par expression.
> 
> Dear Paul,
> can you give a simple example? I cannot see immediately your point because
> of the shared construct.
> 
> Apart from that, I do not like so much the terminology 'instance oriented' and
> 'event oriented' grammar in MSC-96. In fact, my idea was to include the
> 'instance oriented' representation of MSC-92 within the new 'event oriented' representation.
> (since message inputs may appear before corresponding message outputs within this
> 'event oriented' grammar)
> 
> Unfortunately, because of upward compatability  there  still remained this
> <old instance head statement>. Apart from that, I would rather distinguish between
> <shared event> - and <multi instance event> representation (e.g. with respect to
> conditions and inline expressions). I must admit that the <shared event> - representation
> in some parts (e.g. inline expression) resembles the original 'instance oriented'
> representation, in order to avoid the obscuring mixing of events on different instances
> within operator expressions.
> 
> Best regards!
> Ekkart
> 
> =================================================================================
> Dr. Ekkart Rudolph                      phone: +49 89 289 25361
> Technische Universitaet Muenchen        fax:   +49 89 289 28183
> Institut fuer Informatik,               email: rudolphe#informatik.tu-muenchen.de
> c/o Lehrstuhl Prof. Broy
> Arcisstrasse 21
> D - 80290 Muenchen
> =================================================================================
> 
> -----End text from Ekkart Rudolph <rudolphe#informatik.tu-muenchen.de> to mscnews -----
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-----End text from UK496 Paul Baker <paul#bae231.comm.mot.com> to mscnews -----
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