- From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
- Date: 22 Aug 2001 13:27:03 +0100
- To: "Stephane Pageau" <spageau@sed.ara.com>
- Cc: <xmlschema-dev@w3.org>, <jpowell@sed.ara.com>
"Stephane Pageau" <spageau@sed.ara.com> writes:
> How can I construct a XML schema in which
> I wish to enforce that the content
> of an element (e.g., a subelement)
> be an existing element of the instance
> XML file?
> To clarify this question let me take an example:
> ------------------------------------------------
> Assume that I have a shape described using a
> bunch of vertices and I describe both the
> vertices and the shape separately as follows:
> <vertex id=10 >
> <x> 10. </x>
> <y> 60. </y>
> </vertex>
> <vertex id=20 >
> <x> 10. </x>
> <y> 45. </y>
> </vertex>
> <vertex id=30 >
> <x> 10. </x>
> <y> 50. </y>
> </vertex>
> ...
> <shape id=1>
> <vertexptr> 10 </vertexptr>
> <vertexptr> 30 </vertexptr>
> <vertexptr> 20 </vertexptr>
> </shape>
> How can I construct my schema to make sure that someone does not
> put <vertexptr> 1000 </vertexptr> if
> the vertex with id=1000 does not exist?
Sure -- make the content of <vertexptr> be of type IDREF.
As the REC notes, this is not backward compatible with DTDs -- if you
changed to <vertexptr ref="30"/> that would no longer be a problem.
Oops -- you can't use integers as IDs in XML.
So make vertex ids be keys, and the content/ref of vertexptr be
keyrefs. See [1] in the REC or [2] in the Primer.
ht
[1] http://www.w3.org/TR/xmlschema-1/#cIdentity-constraint_Definitions
[2] http://www.w3.org/TR/xmlschema-0/#specifyingUniqueness
--
Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
W3C Fellow 1999--2001, 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/
Received on Wednesday, 22 August 2001 08:26:41 UTC