Chapter 3 Building an XML model
Identity constraints allow you to indicate that element values must be unique within their specified scope.
You can use the Constraints tab of an element property sheet to add the following constraints to an element declaration:
| Tool | Tooltip | Description |
|---|---|---|
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Add Key Constraint | The element value must be a key within the specified scope. The scope of a key is the containing element in an instance document. A key must be unique, not null, and always present |
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Add Unique Constraint | The element value must be unique or null within the specified scope |
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Add KeyRef Constraint | The element value corresponds to those of the specified key or unique constraint |
You can access directly to the Constraints tab of an element property sheet through the contextual menu. Right-click an element symbol in the diagram and select Constraints in the contextual menu.
For more information on constraints, see section Defining identity constraints.
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