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   Re: [xml-dev] XPointer and XML Schema

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Eric van der Vlist <vdv@dyomedea.com> writes:

> On Thu, 2002-07-18 at 15:57, Henry S. Thompson wrote:
> > Sorry not to be clearer, let me try to be as precise as I can.
> > 
> >    *source*---An XML document containing an remote absolute http-scheme
> >    URI reference (call this *ref*) which includes a (shortform) fragment
> >    identifier XYZZY (call this the *idref*)
> There may be cases where there is no XML source then (the reference may
> be located in a HTML document or entered in the URL entry area of a
> browser.

Of course -- I was trying to focus on one representative case.


> > So my basic argument is that since what counts as an ID, and therefor
> > what determines the *actual target*, depends crucially on the
> > *supplementary resources*, and therefor on the *user agent* and its
> > environment, that is user parameterisation/policy specifications,
> > catalogs, caches, proxies, etc.,  the *source* and *target document*
> > necessarily underdetermine the *actual target*.
> I think I get the picture, and I'd just like to illustrate on simple
> example with my own words to make it sure I get it right :-)
> So, the user agent sends a request for the target document to the
> server. 
> If the headers of the answer from the server identifies the target
> document as being XML the user agent knows that the fragment is using a
> XPointer syntax.

Well, strictly speaking this _will_ be the case only if the IETF
accept some version of XPointer as the fragID syntax for the relevant
mime types -- I had been assuming that, but failed to make it

> When this is the case, and when the syntax is shortand, the user agent
> knows that it must find the element identified by the "bare name" and
> may need to construct a PSVI for this if it doesn't find the information
> in the XML infoset of the document.

Not as currently written -- the W3C XML Schema-derived ID-ness takes
precedence, so it needs to know _first_ whether it can and will
schema-validity-assess, before it checks for DTD-derived ID-ness.

> If the user agent has been instructed to use an alternative schema or if
> the user agent has been programed or configure to use an alternative
> schema, it will use this alternative schema to build the PSVI.
> Otherwise it will look for a schema location in the target document.
> If there is no schema location in the target document, it may use any
> kind of black magic to find a schema (dereferencing the namespace URI
> expecting to find a schema or a RDDL document or using any kind of
> directory mechanism).
> If it still has no schema it may raise an error or warning. Otherwise,
> it will build the PSVI and try to match the bare name on the id table. 



> > My answer: Yes, but not in the fragId and it's not the XPointer REC's
> > job.  These questions are clearly the responsibility of XML Processing
> > Model REC (forthcoming, I hope), in my opinion.  Note of course there
> > are typically at least _two_ authors involved, which is another reason
> > why putting it in the fragID is a bad idea.
> My point was not to say to which spec that belongs but to make sure the
> purpose was really to leave the behavior undefined to a certain point!

I would have said, as I did above, 'underdetermined' rather than
'undefined', and emphasised again that this is true for both DTD-based
_and_ schema-based ID-ness, but I think we're on the same page here.


> Thanks for these clarifications!

You're welcome.  Thank _you_ for your careful question, which helped
me to clarify my own thinking.

  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2002, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/
 [mail really from me _always_ has this .sig -- mail without it is forged spam]


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