203   <xs:unique>

Created: 13 Sep 2005

Status: Not Applicable

Part: Part 6 (2004)



Clause: General


Category: Issue for edition 2 of this part


<xs:unique> requires that any attributes referenced in the field are non-null. Validators give inconsistant results and typically fail to flag unicity errors when these attributes are missing. SCL contains a few <xs:unique> definitions that contain fields that reference optional attributes. They are UniqueLNodeType, UniqueLNInAccessPoint, UniqueLNInDevice and UniqueLNode.


Any attribute referenced in a <xs:unique> field should be required. This would affect tLNode, tLN and tLNodeType.

Discussion Created Status
The statement is not quite correct. SCL is based on XML version 1.0, which says the following:
From "XML Schema Part 1: Structures" (http://www.w3.org/TR/xmlschema-1/):
(unique) the Identity-constraint definition asserts uniqueness, with respect to the content identified by {selector}, of the tuples resulting from evaluation of the {fields} XPath expression(s).
(key) the Identity-constraint definition asserts uniqueness as for unique. key further asserts that all selected content actually has such tuples.

This means, that attributes used in unique statements are allowed to be missing (i.e. null), in contrast to key values. Therefore, no changes are necessary.
15 Sep 05 Not Applicable


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