XML Schema keyElement

XML Schema 参考手册Complete XML Schema Reference

Definition and Usage

The key element specifies that an attribute or element value (or a set of values) must be a key within a specified scope. The scope of the key is the containing element in the instance document. Key means that the data should be unique, non-zero, and always present within the specified scope.

The key element must contain the following elements in order:

  • The selector element contains an XPath expression that specifies a set of elements, within which the values specified by field must be unique.

Element Information

  • Parent element: element

Syntax

<key
id=ID
name=NCName
any attributes
>

(annotation?,(selector,field+))

</key>

(The ? sign declares that the element can appear zero or one time inside the key element, and the + sign declares that the element must appear one or more times.)

Attributes Description
id Optional. Specifies a unique ID for the element.
name Required. Specifies the name of the key element.
any attributes Optional. Specifies any other attributes with a non-schema namespace.

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