XML Schema attribute Element
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Definition and Usage
The attribute element defines an attribute.
Element Information
- Parent elements: attributeGroup, schema, complexType, restriction (both simpleContent and complexContent), extension (both simpleContent and complexContent)
Syntax
<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 ? sign declares that the element can occur zero or one time inside the attribute element)
| Attribute | Description |
|---|---|
| default | Optional. Specifies a default value for the attribute. Default and fixed attributes cannot both be present |
| fixed | Optional. Specifies a fixed value for the attribute. Default and fixed attributes cannot both be present |
| form | Optional. Specifies the form for the attribute. The default value is
the value of the attributeFormDefault attribute of the element
containing the attribute. Can be set to one of the following:
|
| id | Optional. Specifies a unique ID for the element |
| name | Optional. Specifies the name of the attribute. Name and ref attributes cannot both be present |
| ref | Optional. Specifies a reference to a named attribute. Name and ref attributes cannot both be present. If ref is present, simpleType element, form, and type cannot be present |
| type | Optional. Specifies a built-in data type or a simple type. The type attribute can only be present when the content does not contain a simpleType element |
| use | Optional. Specifies how the attribute is used. Can be one
of the following values:
|
| any attributes | Optional. Specifies any other attributes with 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 example above indicates that the "code" attribute has a restriction. The only acceptable value is two of the uppercase letters from a to z.
Example 2
To declare an attribute using an existing attribute definition within a complex type, use the ref attribute:
<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
Attributes can have either a default value OR a fixed value specified. A default value is automatically assigned to the attribute when no other value is specified. In the following example the default value is "EN":
<xs:attribute name="lang" type="xs:string" default="EN"/>
A fixed value is also automatically assigned to the attribute when no other value is specified. But unlike default values; if you specify another value than the fixed, the document is considered invalid. In the following example the fixed value is "EN":
<xs:attribute name="lang" type="xs:string" fixed="EN"/>
Example 4
All attributes are optional by default. To explicitly specify that the attribute is optional, use the "use" attribute:
<xs:attribute name="lang" type="xs:string" use="optional"/>
To make an attribute required:
<xs:attribute name="lang" type="xs:string" use="required"/>
❮ Complete XML Schema Reference
