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Re: URN ID syntax and XML Schema

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 24 Jan 2003 10:41:02 +0000
To: "Nikola" <nikola.stojanovic@acm.org>
Cc: <www-xml-schema-comments@w3.org>
Message-ID: <f5bvg0e4ypt.fsf@erasmus.inf.ed.ac.uk>

"Nikola" <nikola.stojanovic@acm.org> writes:

> I have a question related to ID syntax and how XML Schema constraints it
> usage in XML instance documents. I have searched archives, but couldn't find
> any explanation (examples, ...) that justify this constrant in XML Schema.
> Here is a simple schema and an instance document that uses
> "urn:uuid:f3373a7b-4958-4e55-8820-d03a191fb76a" as an example of an ID.


> My understanding of XML 1.0
> (http://www.w3.org/TR/2000/WD-xml-2e-20000814#NT-Name) is that ID can have
> ":" characters, but XML Schema (http://www.w3.org/TR/xmlschema-2/#ID)
> restricts this by forbiding the usage of ":" character
> (http://www.w3.org/TR/1999/REC-xml-names-19990114/#NT-NCName). In this way
> URN syntax is not allowed in XML Schema ID.
> I suspect that this might be Namespace Recommendation issue

It is indeed -- see [1], the last paragraph.

There has been lengthy discussion about this, and the forthcoming
publication of Namespaces 1.1 will clarify the terminology, but not in
such as was as to suggest that Schema will chnge in this area.

> but could (should) this XML Schema constraint be relaxed in the
> future

This is unlikely, in my opinion.

> or there would be (is) a way to build upon XML Schema type hierarchy
> and still have IDREF semantics checked by validators when ID needs
> to be compliant to URN syntax?

Absolutely -- use key/keyref, and declare your attributes to have
whatever type you think appropriate (e.g. xs:anyURI plus a
'urn:uuid:[-0-9a-f]*' pattern).


[1] http://www.w3.org/TR/1999/REC-xml-names-19990114/#Conformance
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
                      Half-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/
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Received on Friday, 24 January 2003 05:40:53 UTC

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