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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:
  • "qualified" - indicates that this attribute must be qualified with the namespace prefix and the no-colon-name (NCName) of the attribute
  • unqualified - indicates that this attribute is not required to be qualified with the namespace prefix and is matched against the (NCName) of the attribute
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:
  • optional - the attribute is optional (this is default)
  • prohibited - the attribute cannot be used
  • required - the attribute is required
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