<xsd:field> Element

Specifies an XML Path Language (XPath) expression that specifies the value (or one of the values) used to define an identity constraint (unique, key, and keyref elements).

<field
  id = ID 
  xpath = a subset of XPath expression 
  {any attributes with non-schema Namespace}...>
Content: (annotation?)
</field>

Attributes

• id
  The ID of this element. The id value must be of type ID and be unique within the document containing this element.

  Optional.

• xpath
  An XPath expression that is relative to each element selected by the selector of the identity constraint. This expression must identify a single element or attribute whose content or value is used for the constraint. If the expression identifies an element, that element must be of a simple type.

  Required.

Element Information

Remarks

An identity constraint must contain one or more field elements and those field elements must appear after the selector element.

Selector ::= Path ( '|' Path )*  
FieldXPath ::= ('.//')? ( Step '/' )* ( Step | '@' NameTest )  
Step ::= '.' | NameTest  
NameTest ::= QName | '*' | NCName ':' '*'  

Remarks

Note
When using XPath, you must use fully qualified names if the name is defined with a non-empty targetNamespace. For example, myNS:localName instead of localName.

Example

The following fragment is a field element that specifies the myID attribute as the field to use for the identity constraint.

<xs:field xpath="@myID"/>

Other Resources

For more information see the W3C XML Schema Part 1: Structures Recommendation.

See Also

Reference

XML Schemas (XSD) Reference
XML Schema Elements