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Re: null and keyref

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 16 May 2000 16:51:46 +0100
To: petsa@us.ibm.com
Cc: www-xml-schema-comments@w3.org
Message-ID: <f5bvh0ecx2l.fsf@cogsci.ed.ac.uk>
petsa@us.ibm.com writes:

> Your note of 4/12 reproduced below confuses me.
> keyref fields can only refer to key fields and these are, by definition,
> non-nullable.

> Referenced note
> =============================

> Not key, but keyref, for a change.  Seems to me we missed a case: if
> the node picked out by a keyref's field is xsi:null='true', then
> this should be treated as if the node had not been found. As the PWD
> reads, it will just use an empty string as that field's contribution
> to the key sequence to be looked up.  Ditto for unique fields.

As the spec. stands, only the fields of keys as such must be
non-nullable.  The fields of uniques and keyrefs may be nullable, and
hence may be xsi:null='true' and lack values.  I'd rather say
explicitly that in the case of unique this means the element in
question has no key-sequence, and that in the case of keyref that the
keyref is broken, rather than just use the empty string as (part of) the 
key-sequence in either case.

  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 Tuesday, 16 May 2000 11:51:56 UTC

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