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Re: Questions on event values

From: Lloyd Rutledge <Lloyd.Rutledge@cwi.nl>
Date: Mon, 22 Mar 1999 18:03:38 +0100
Message-Id: <UTC199903221703.SAA15820.lloyd@klipper.cwi.nl>
To: Leandro Marques Rodrigues <leandro@telemidia.puc-rio.br>, www-smil <www-smil@w3.org>

On Thu, Mar 18 1999 Leandro Marques Rodrigues wrote:

> Imagine if the element E1 is
> declared after the element that references it, for example:
> <seq>
>    <ref begin="id(E1)(begin)" ... />
>    <ref id="E1" .../>
>    ...
> </seq>
> The beggining of the first element depends on the beggining of E1, but
> the beggining of E1 depends on the end of the first element. So, how
> would the element seq behave?

Such cyclic dependencies are clearly errors.  The solution here is
simply for authors to avoid cyclic sychronizations relationships.

> For me, the explicit begin of a child of a seq element should be
> specified only related to the effective end of its ancestor (or the

This doesn't make sense.  The ancestor would be the <seq>.  Do you
mean to refer instead to its previous sibling?

> effective begin of the seq element, if it is its first child), and the
> explicit begin of a child of a par element should be specifed only
> related to the effective begin of the par element itself or of any other
> child.

What you describe are the typical situations for which synchronization
would be used on the children of <seq>'s and <par>'s.  It is for this
reason that what you describe is the default interpretation of the
values of begin and end attributes when they are simply delay values.
It seems that what you are arguing for is, using the language of the
spec, the removal of "element-event values" (relative synchronization)
from begin and end attributes.  Clearly, for the sitations you
describe, authors should use delay values, which is what they are
there for.  But presentations do often have more complex
synchronizations needs for which element-event values are appropriate.


Lloyd Rutledge                              vox: +31 20 592 41 27
CWI (Centrum voor Wiskunde en Informatica)  fax: +31 20 592 41 99
PO Box 94079                                net: Lloyd.Rutledge@cwi.nl
NL-1090 GB Amsterdam, The Netherlands       Web: http://www.cwi.nl/~lloyd
Received on Monday, 22 March 1999 12:03:44 UTC

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