15.2.55. XML Schema unique element

Definition and usage ¶

The unique element specifies that an attribute or element value (or a combination of attribute or element values) must be unique within a specified range. The value must be unique or zero.

The unique element must contain the following elements in order:

The oselector element contains an XPath expression that specifies a set of elements in which the value specified by the field element must be unique. There must be one and only one selector element.

Each field element contains an XPath expression that specifies a value (attribute or element value) that must be unique to the set of elements specified by the selector element. If there are multiple field elements, the combination of field elements must be unique. In this case, the value of a single field element may not be unique to the selected element, but the combination of all fields must be unique. There must be one or more field elements.

Element information ¶

父元素： Element

Grammar ¶

<unique
id=ID
name=NCName
*any attributes*
>
(annotation?,(selector,field+))
</unique>

(? The symbol declares that the element can appear zero or once in the unique element. )

Attribute	Description
Id	Optional. Specifies the unique ID of the element.
Name	Necessary. Specify a name for the element.
Any attributes	Optional. Specifies any other attributes with the non-schema namespace.

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