XML Pocket Reference, 3rd Edition

Name

xs:key

Attributes

name

A name for the key (not namespace qualified, as it uses the namespace of the schema)

Contents

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

xs:key lets you state that parts of a document must have specific values unique across the set of parts for the document to be valid. An xs:key element uses the XPath value in an xs:selector element to identify where the key applies, and the xs:field element to specifically identify which part of the document must be both present and unique among those values.

xs:key 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:key behaves exactly like xs:unique, except that xs:unique does not require the values it identifies to be present.