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Re: QName URI Scheme Re-Visited, Revised, and Revealing (was RE: De dicated, Standardized URI Scheme for QNames?)

From: Dan Connolly <connolly@w3.org>
Date: Thu, 23 Aug 2001 09:14:55 -0500
Message-ID: <3B850FDF.9FA0391E@w3.org>
To: Patrick.Stickler@nokia.com
CC: sean@mysterylights.com, www-rdf-interest@w3.org, www-rdf-logic@w3.org
Patrick.Stickler@nokia.com wrote:
[...]
> I re-re-read the
> XML NS spec and Sean is quite right about the QName partitions being
> a component of the lexical identity (though I wonder what the significance
> is of those partitions being non-normative...) That information should,
> I fully agree, be embodied in some way in any alternate representation
> of QNames that exists outside the scope of the serialized instance
> in which they occur.

As you observed, that appendix is non-normative. But it
makes clear that the designers of the spec didn't intend
for there to be a function from QNames alone to referents/resources.
It makes clear that in the general case, you need more
context info to tell what a QName denotes.

In other words, the XML namespaces spec doesn't actually
specify the structure of an XML namespace! We considered
changing the name, but it had momentum...

The bottom line is: in general, QNames don't work like URIs;
their scope is not the global internet scope; their scope depends
on how you use them. XML Schemas allow the meaning
of a QName to depend on the parent elements, for
example.

If you're suggesting that each spec that uses QNames should
say how to map them to URIs, I heartily agree! I tried
to get XML Schema types and such to be named with URIs,
but I couldn't convince the WG it was worthwhile. I believe
the WG is still considering it, in the course of the
development of the formal description for XML Schemas.
Ah! indeed:

"The goals of the formalization are to:
     [...]
     Specify names for all components of an XML Schema, so that they can
     be uniquely identified by URIs. Such unique identifiers may be
useful to
     XML Query, RDF, and topic maps, among others. "
	-- XML Schema: Formal Description
	W3C Working Draft, 20 March 2001
	http://www.w3.org/TR/2001/WD-xmlschema-formal-20010320/

But if you're looking for a single mapping from QNames
to URIs, there isn't one that's consistent with
all of XSLT, RDF, and XML Schemas. Perhaps it's worth
taking the time to design one that does work, but I'm
pretty sure you'll have to do some substantial
redesign of at least one of those three, and I'm
not sure that's worthwhile.

[...]
> Two questions can IMO direct this issue one way or another:
> 
> 1. Can a QName used in one partition represent semantics that is not
> equivalent
> to the semantics attributed to the same QName in another partition?

In the general case, where a "partition" can be any sort
of structure, yes, the same QName can denote different
things for any sort of reason at the whim of the designer
of the XML sublanguage.

> I.e. can an element <foo:bar> a global attribute <... foo:bar="..."> and
> a per-element attribute <... bar="..."> all mean different things?

Yes.

> 2. And if so, is RDF required to maintain that distinction?

No.


-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 23 August 2001 10:15:06 GMT

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