XML Pocket Reference, 3rd Edition

Name

xs:unique

Attributes

name

A name for the key (not namespace-qualified)

Contents

xs:annotation?, (xs:selector, xs:field+)

xs:unique lets you state that parts of a document must have values unique across the set of parts for the document to be valid. An xs:unique element uses the XPath value in an xs:selector element to identify where the constraint applies and the xs:field element to specifically identify which part of the document must be unique among those values. (Values may also be missing.)

xs:unique elements may appear only as children of xs:element. The xs:selector XPaths are calculated from the element in which the key is defined, while the xs:field XPaths are calculated from the selector. The name attribute is used for identification with xs:keyref. Also, xs:unique behaves exactly like xs:key, except that xs:key requires the values it identifies to be present.