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XML Schema key Element


XML Schema Reference Complete XML Schema Reference

Definition and Usage

The key element specifies an attribute or element value as a key (unique, non-nullable, and always present) within the containing element in an instance document.

The key element MUST contain the following (in order):

  • one and only one selector element  (contains an XPath expression that specifies the set of elements across which the values specified by field must be unique)
  • one or more field elements (contains an XPath expression that specifies the values that must be unique for the set of elements specified by the selector element)

Element Information

  • Parent elements: element

Syntax

<key
id=ID
name=NCName
any attributes
>

(annotation?,(selector,field+))

</key>

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

Attribute 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 non-schema namespace

XML Schema Reference Complete XML Schema Reference