Identity Constraint Definition ( Schema Component Definition Component Secondary Component )
Identity Constraint Definition
Identity-constraint Definitions
Subject Indicators
An identity-constraint definition is an association between a name and one of several varieties of identity-constraint related to uniqueness and reference. All the varieties use XPath expressions to pick out sets of information items relative to particular target element information items which are unique, or a key, or a ·valid· reference, within a specified scope. An element information item is only ·valid· with respect to an element declaration with identity-constraint definitions if those definitions are all satisfied for all the descendants of that element information item which they pick out.