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Identity Constraints

From: Mark Thornton <mthornton@optrak.co.uk>
Date: Thu, 7 Mar 2002 17:08:04 -0000
Message-ID: <30273167BD5AD111A5AD00A0C9922017537463@mercury.net.optrak.co.uk>
To: "'xmlschema-dev@w3.org'" <xmlschema-dev@w3.org>
I am rather confused by some types of multi field identity constraints. The
example in the schema primer: (at
http://www.w3.org/TR/xmlschema-0/#specifyingUniqueness)

<unique name="dummy1">
  <selector xpath="r:regions/r:zip"/>
  <field    xpath="@code"/>
  <field    xpath="r:part/@number"/>
 </unique>

seems to be what I want, BUT I can't reconcile this with the validation
rules in the standard (3.11.4):

"3 For each node in the Ětarget node setĚ all of the {fields}, 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."

Specifically the second field would appear to have multiple values for a
single node in the target set (a 'zip' element).

Is there a good explanation anywhere of the use of identity constraints
where the fields are not all at the same depth?

Thanks for any help,
Mark Thornton
Received on Thursday, 7 March 2002 12:08:35 GMT

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