Defining Identity Constraints; Defining A Unique Constraint - Sybase PowerDesigner XML User Manual

Defining identity constraints

Defining identity constraints

Defining a unique constraint

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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.
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:
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