15.2.56. XML Schema attribute element

Definition and usage ¶

The attribute element defines an attribute.

Element information ¶

父元素： AttributeGroup, schema, complexType, restriction (both simpleContent and complexContent), extension (both simpleContent and complexContent)

Grammar ¶

<attribute
default=string
fixed=string
form=qualified|unqualified
id=ID
name=NCName
ref=QName
type=QName
use=optional|prohibited|required
*any attributes*
>
(annotation?,(simpleType?))
</attribute>

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

Attribute	Description
Default	Optional. Specifies the default value for the property. The default and fixed properties cannot appear at the same time.
Fixed	Optional. Specifies the fixed value of the attribute. The default and fixed properties cannot appear at the same time.
Form	Optional. Specifies the format of the attribute. The default value is the value of the attributeFormDefault attribute of the schema element that contains the attribute. Can be set to the following values: “qualified”-indicates that this attribute must be qualified by the namespace prefix and the non-colon name (NCName) of the attribute. “unqualified”-indicates that this property does not need to be qualified by a namespace prefix and does not need to match the non-colon name (NCName), the local name, of this attribute.
Id	Optional. Specifies the unique ID of the element.
Name	Optional. Specifies the name of the attribute. The name and ref properties cannot appear at the same time.
Ref	Optional. Specifies a reference to the specified property. The name and ref properties cannot appear at the same time. If ref appears, the simpleType element, form, and type cannot appear.
Type	Optional. Specify built-in data types or simple types. The type attribute can only appear if the content does not contain a simpleType element.
Use	Optional. Specifies how to use this property. The following values can be set: Optional-the attribute is optional and can have any value (default). Prohibited-attributes cannot be used. Required-required for the attribute.
Any attributes	Optional. Specifies any other attributes with the non-schema namespace.

Example 1 ¶

<xs:attribute name="code">
<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="[A-Z][A-Z]"/>
  </xs:restriction>
</xs:simpleType>
</xs:attribute>

The above example indicates that the “code” property has a qualification. The only acceptable values are the two letters in the uppercase letters A to Z.

Example 2 ¶

To declare a property using an existing property definition in a complex type, use the ref property:

<xs:attribute name="code">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:pattern value="[A-Z][A-Z]"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>
<xs:complexType name="someComplexType">
  <xs:attribute ref="code"/>
</xs:complexType>

Example 3 ¶

Property can have either a default value or a specified fixed value. When no other value is specified, the default value is automatically assigned to the property. In the following example, the default value is “EN”:

<xs:attribute name="lang" type="xs:string" default="EN"/>

When no other value is specified, a fixed value is automatically assigned to the property. However, unlike the default value, if you specify a value other than a fixed value for the property, the document is validated as invalid. In the following example, the fixed value is “EN”:

<xs:attribute name="lang" type="xs:string" fixed="EN"/>

Example 4 ¶

All properties are optional by default. To explicitly specify that the property is optional, use the “use” attribute:

<xs:attribute name="lang" type="xs:string" use="optional"/>

To make an attribute a required attribute:

<xs:attribute name="lang" type="xs:string" use="required"/>

XML Schema 参考手册完整 XML Schema 参考手册