Name

xs:unique

Synopsis

<xs:unique
  id = "ID"
  name = "NCName" >
  <!-- (xs:annotation?, xs:selector, xs:field+ ) -->
</xs:unique>

The xs:unique element requires that a specified subset of elements and/or attributes in the instance document have unique values calculated from each of those elements/attributes. This is similar to the constraint imposed by declaring an attribute to have type xs:ID, but it is much more flexible. The xs:selector child element uses XPath to specify the subset of nodes from the instance document over which uniqueness is calculated. The xs:field children use XPath expressions to specify what properties of those nodes must be unique within the subset.