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Defining identity constraints
64 PowerDesigner
Defining identity constraints
Identity constraints enable you to indicate that element values must be unique
within their specified scope.
There are three kinds of identity constraints: unique, key and keyRef.
Each identity constraint has two specific attributes: selector and field.
In a schema, an identity constraint is declared with its corresponding tag:
<unique>, <key> or <keyRef>.
Identity constraints are only available in a model targeted with XSD.
Defining a unique constraint
A unique constraint specifies that an element or an attribute value (or set of
values) must be unique or null within a specified scope.
For example:
Generated schema: