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Unique constraint.

From: Tishkin, Eugene <etishkin@mackenziefinancial.com>
Date: 05 Dec 2005 16:05:32 -0700
Message-ID: <9685B8A36EB4A344A2AD0CC3508262C8B8B917@MFMAILEVS1.mackenziefinancial.bz>
To: <www-xml-schema-comments@w3.org>


Proposed change for the definition is:

3.11.4 Identity-constraint Definition Validation Rules

4.1.1 The  <http://www.w3.org/TR/xmlschema-1/#key-tns> ·target node set· is a subset of the   <http://www.w3.org/TR/xmlschema-1/#key-qns> ·qualified node set·, that is, every member of the  <http://www.w3.org/TR/xmlschema-1/#key-tns> ·target node set· is also a member of the  <http://www.w3.org/TR/xmlschema-1/#key-qns> ·qualified node set· however not every member of   <http://www.w3.org/TR/xmlschema-1/#key-qns> ·taget node set· is a member of  <http://www.w3.org/TR/xmlschema-1/#key-qns> ·qualified node set·.

Why this is important?

Xerces parser has a bug 18405, which has not been resolved since 2003.
The reason for not fixing is :
" ... I (and some others I've asked) think
that the spec seems open to interpretation here; so I'm marking this bug
invalid for now.  I'd encourage you to pose a question to the Schema working
group via their comments list; if you get a response that demonstrates that
your reading is correct, please reopen this bug with the appropriate text and
I'll try and fix it when I get a chance."

The below is the comment from Xerces parser BUG 18405 report:
"3 For each node in the
·target node set·
all of the
with that node as the context node, evaluate to either an empty node-set or a
node-set with exactly one member, which must have a simple type."

The target node set is the set of nodes on which the selector is matched.  Note
that this condition must hold for *any* identity constraint; only in bullet 4
of the tableau are the differences between key and unique described. 
Therefore, it seems clear that, if a selector matches, then either all of the
fields must match or none of them must match; even for xsd:unique, you can't
have some fields matching.


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Received on Monday, 5 December 2005 23:08:10 UTC

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