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SYMM WG comments on XBase 2nd last call

From: Lloyd Rutledge <Lloyd.Rutledge@cwi.nl>
Date: Wed, 28 Jun 2000 12:27:57 +0200
Message-Id: <200006281027.MAA11188@spruit.cwi.nl>
To: www-xml-linking-comments@w3.org
The SYMM WG has generated the following comments on the XBase 2nd last
call.  This is our official response:

Having multiple XBases in one document would be helpful.  For example,
this would allow media objects of different types to be located on
different directories or from different servers -- currently a common
practice.  XBase provides this through hierarchical inheritance and by
allowing xbase attribute assignments to be entities.

XBase assignments are inherited by descendants.  That is, the xbase
attribute can be on any element, and it applied to all attributes with
relative URI's on that element and all its descendants.  Assigning
this attribute to an element overrides any xbase attributes assigned
to any of its ancestors.  For this use to work for the above work case,
the author needs to group media objects with the same XBase on the
same branch of the timing model, which is often not practical in SMIL.

Different media object elements strewn through the temporal hierarchy
can be assigned the same XBase by establishing entities and having the
attribute values be these entities.  One could, for example, have a
bunch of entity assignments at the beginning of a document, and then
these could be referred to by xbase attributes throughout the
document.  This means, of course, that is a storage site on the Web
for a collection of videos is changed, this URL only needs to be
changed once in each document that uses videos from this collection.

ATTLIST declarations can defined be in SMIL document instances to
provide a similar function.  With this technique, the xbase attribute
for a particular element type could be defaulted or fixed to a
particular URL.  For example, all <video> elements in a SMIL
presentation could have their "xbase" attribute fixed to a value with
such an ATTLIST assignment.  Alternatively, this assignment could be a
default, in which case individual <video> elements could override it
with their own xbase.

While the two techniques described above may work, we would prefer a
cleaner, more direct means of having different XBases distributed
throughout the document hierarchy.

Therefore, the SYMM working group has the following comments on XBase:

1) XBase as a recommendation fits into SMIL because SMIL is XML. We will not
make any specific restrictions on the use of XBase with SMIL. 

2) We request the SML Linking WG to consider adding referential XBase
functionality to the current draft, or a later version. We will not make
this a requirement for using XBase with SMIL, however.

3) If the XBase recommendation does not have referential functionality, then
we may use XBase and add SMIL specific referential functionality to it.


Lloyd Rutledge  vox: +31 20 592 41 27       fax: +31 20 592 41 99
CWI             net: Lloyd.Rutledge@cwi.nl  Web: http://www.cwi.nl/~lloyd
Post:   PO Box 94079   |  NL-1090 GB Amsterdam  |  The Netherlands
Street: Kruislaan 413  |  NL-1098 SJ Amsterdam  |  The Netherlands
Received on Wednesday, 28 June 2000 06:27:59 UTC

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