Re: SYMM WG comments on XBase 2nd last call

On Fri, Jun 30 2000 Jonathan Marsh wrote:

> Lloyd wrote:
> > 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. 
> 
> I'm glad to hear this, although I'm not sure it will provide you with XML
> Base functionality.  If relative SMIL media URLs are to be resolved against
> xml:base attributes, the SMIL spec must state this explicitly. 

If SMIL uses XBase, the specification will state this explicitly.

> XML Base
> provides a means for specifying the base URI, but not for recognizing URLs
> in arbitrary XML content.  To support XML Base, the SMIL spec should
> identify which attribute values and content represent URIs and state
> explicitly that XML Base should be honored when dereferencing these URIs.
> As an example, xlink:href attribute values are recognized as URIs and the
> XLink spec states that they are resolved against xml:base.

Thanks for the comment.  I will propose to the SYMM WG that the SMIL
specification will identify such attribute values and content if SMIL
uses XBase.

> > 2) We request the XML 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.
> 
> I presume this emerges from the desire to provide multiple "classes" of base
> URI in a document - something akin to xml:video-base, xml:audio-base,
> xml:stylesheet-base.  Admittedly the structure of the XML document will
> often not have a 1-1 correspondence with the desired hierarchy of base URIs.
> The linking WG considered this capability and for simplicity stuck with a
> single generic base.  We will reexamine this issue in light of your request.

Your prose describes the problem well.

> Does the following syntax proposal illustrate your request?
> 
>   <a xml:base="http://www.media.com">
>     <mediabase id="video" xml:base="/daily/video"/>
>     <mediabase id="audio" xml:base="/daily/audio"/>
>     <b xml:baseref="video">vid1</b>
>     <c xml:baseref="audio">aud1</c>
>   </a>
> 
> b = http://www.media.com/daily/video/vid1
> c = http://www.media.com/daily/audio/aud1
> (and "id" is of type ID).

I'd rework the syntax as:

<head>
  <xml:base id="video" xml:base="/daily/video"/>
  <xml:base id="audio" xml:base="/daily/audio"/>
</head>
<body>
  <par>
    <video xml:baseref="video" src="billwaves.mpg"/>
    <audio xml:baseref="audio" src="billtalks.au"/>
  </par>
</body>

> Of course, there are circularity problems with this particular approach...

... can you elaborate?

> > 3) If the XBase recommendation does not have referential
> > functionality, then we may use XBase and add SMIL specific
> > referential functionality to it.
> 
> XML Base is designed to be available generically to text/xml and
> application/xml documents.  If SMIL is using a different media type, it can
> describe any mechanism for embedding base URIs in the document that it
> wants.  If however, you plan to deliver SMIL documents as either text/xml or
> something like text/smil-xml then it seems like even non-text/xml SMIL
> documents should recognize XML Base, and only XML Base, to retain
> interoperability.
> 
> At this point I don't see how augmenting XML Base could work, although I
> look I look forward to any ideas you have on the subject.

We would not augment XML Base.  We would add SMIL-specific and
SMIL-only constructs to SMIL's use of XML Base.  That is, we would use
the XBase constructs of non-referential establishing of URI bases.
And we would dot all the XML i's and cross all the XML t's in doing so
(so we hope ;).  For referential URI bases, we would make SMIL
constructs such as those used in the example syntax above.  This would
existing in the SMIL namespace and would not be recognized as XBase.
Their behavior would be stated in the SMIL specification.

This would mean that SMIL browsers would resolve different URI's than
non-SMIL XBase-aware XML processors would.

-Lloyd

--
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 Monday, 3 July 2000 05:04:37 UTC