XML Schema field element
Definition and Usage
The field element specifies an XPath expression, which specifies the value (or one of the values) used to define the identifier constraint (unique, key, and keyref elements).
element information
occurrence times | once |
parent element | key, keyref, unique |
content | annotation |
syntax
<field id=ID xpath=XPath expression any attributes > (annotation?) </field>
Attribute | Description |
---|---|
id | Optional. Specifies a unique ID for the element. |
xpath | Required. Identifies a single element or attribute whose content or value is used for constraints. If the expression identifies an element, then the element must be of a simple type. |
xml:lang | Optional. Specifies the language used in the content. |
(The '?' symbol is declared within the field element, which can appear zero or one time.)
Instance
Example 1
The following example shows a field element that defines the "userID" attribute as a field used for identification constraints:
<xs:field xpath="@userID"/>