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Re: discussion about temporal scenario modelisation

From: Cecile Roisin <Cecile.Roisin@imag.fr>
Date: Thu, 05 Mar 1998 10:30:02 +0100
Message-Id: <199803050930.KAA08639@perles.inrialpes.fr>
To: Warner ten Kate <tenkate@natlab.research.philips.com>
cc: Muriel.Jourdan@imag.fr, Cecile.Roisin@imag.fr, www-multimedia@w3.org

Once again, sorry for the delay ...

In order to be easily understood the discussion, i make a short resume
of the previous emails. I hope that i did not make wrong
interpretations.

The problem was to see how some constraints specification could be
expressed in SMIL. The example was :
A meets B
B meets C
I starts A

 One solution suggested by Warner ten Kate is to use synchronisation
events :

<par>
  <B begin="id(A)(end)"/>
  <C begin="id(B)(end)"/>
  <I />
  <A begin="id(E)(end)"/>
</par>

We'd like to make three main answers :

1) It seems to us difficult for the author (lisibility and reuse) to
handle such kind of specifications where the par operator looses its
semantics due to event-synchronisation.

2) Constraints do not forced a direction between the time points :
I starts A is equivalent to begin(I) = begin(A) (this is a real =  and
not a => as in the SMIL specification).

3) We think that the main interest provided with constraints is given by the 
ability to let the system (or more precisely the temporal formatter) compute a 
solution from the specifications (i.e. affect dates and durations to objects). 
It is clear that such a work can be done by the author but it is much more 
bothering.

We now answer on some local points :

Warner ten kate wrote :
>> 
>> Suppose now that A and B are two moving objects which have to reach some
>> different fixed points on the screen. In addition the author can adjust
>> their speed as he wants.
>> 
>> The semantic expressed by A equal B is: A and B starts and finishes at
>> the same time, and none of them has been interrupted (i.e they reached
>> their final position).
>> With a constraint-based approach the temporal formatter chooses a
>> well-suited speed for each objects.

>I am a little confused: does A equal B specify that both objects are 
>of equal duration, or does it specify that the dynamic actions applied 
>on them (move the objects) are of equal duration?

The two propositions are true : A equals B means that both objects are 
of equal duration and that the dynamic actions applied on these objects
are of equal duration. This is not always a satisfying solution so we
study how to separate the duration of a dynamic style to the
presentation duration. Moreover we want to be able to synchronize the
two kinds of time interval. For instance to express that two video are
presented at the same time and when the first one finishes, the other
one moves on the screen as far as it reachs its end.

> assume A is of shorter duration than B and "A equal B" is 
> specified, how is it decided if A is to be stretched, or B to 
> be shrinked, or both A stretching and B shrinking? Or do have 
> "A equal B" and "B equal A" different semantics? They have not 
> in Allen's description, have they?.

For the moment, in Madeus the author has no way  to express a preference
on these two solutions. Such mechanisms were experimented in Firefly. 

>PS. I am interested to learn about the logical grouping in Madeus. 
> Is it possible for you to answer my questions?

> Warner ten Kate wrote:
> > What I get from the figures in your document, in Madeus you
> > specify constraints between media-objects; sets of media-objects
> > with their constraints can be taken together into logical groups.
> >
> > Is this correct?

Yes 

> > Is there any additional semantics to these logical groups
> > eg. are there (structured) dependicies between these groups?


In Madeus we take the problem in the reverse order. The author defines a
hierarchy of nested object (logical group structured by a contain
relation). Then he could set temporal constraint between objects (basic
or composite ones) which have the same father in the hierarchy. This
allows to easily reuse a composite object.
However, this is not always a satisfying solution (sometimes the author would 
like to put temporal constraints between non-siblings objects) and we would 
like to study (but the time is missing ...) how to give a real logical 
dimension
to a multimedia document without being in conflict with the temporal 
dimension. 

Kind regards,

Cecile Roisin and Muriel Jourdan


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Cecile Roisin,  Muriel Jourdan
EMAIL: Cecile.Roisin@inrialpes.fr Muriel.Jourdan@inrialpes.fr
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Received on Thursday, 5 March 1998 04:31:36 UTC

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