Table of contents

Appendices

3.2 Qualified Locals

Elements and attributes can be independently required to be qualified, although we start by describing the qualification of local elements. To specify that all locally declared elements in a schema must be qualified, we set the value of elementFormDefault to qualified:

NOTE: 

Modifications to po1.xsd for Qualified Locals

<schema xmlns="http://www.w3.org/2001/XMLSchema"
        xmlns:po="http://www.example.com/PO1"
        targetNamespace="http://www.example.com/PO1"
        elementFormDefault="qualified"
        attributeFormDefault="unqualified">

  <element name="purchaseOrder" type="po:PurchaseOrderType"/>
  <element name="comment"       type="string"/>

  <complexType name="PurchaseOrderType">
    <!-- etc. -->
  </complexType>

  <!-- etc. -->

</schema>

And in this conforming instance document, we qualify all the elements explicitly:

NOTE: 

A Purchase Order with Explicitly Qualified Locals

<?xml version="1.0"?>
<apo:purchaseOrder xmlns:apo="http://www.example.com/PO1"
                   orderDate="1999-10-20">
  <apo:shipTo country="US">
    <apo:name>Alice Smith</apo:name>
    <apo:street>123 Maple Street</apo:street>
    <!-- etc. -->
  </apo:shipTo>
  <apo:billTo country="US">
    <apo:name>Robert Smith</apo:name>
    <apo:street>8 Oak Avenue</apo:street>
    <!-- etc. -->
  </apo:billTo>
  <apo:comment>Hurry, my lawn is going wild<!/apo:comment>
  <!-- etc. -->
</apo:purchaseOrder>

Alternatively, we can replace the explicit qualification of every element with implicit qualification provided by a default namespace, as shown here in po2.xml:

NOTE: 

A Purchase Order with Default Qualified Locals, po2.xml

<?xml version="1.0"?>
<purchaseOrder xmlns="http://www.example.com/PO1"
               orderDate="1999-10-20">
  <shipTo country="US">
    <name>Alice Smith</name>
    <street>123 Maple Street</street>
    <!-- etc. -->
  </shipTo>
  <billTo country="US">
    <name>Robert Smith</name>
    <street>8 Oak Avenue</street>
    <!-- etc. -->
  </billTo>
  <comment>Hurry, my lawn is going wild<!/comment>
  <!-- etc. -->
</purchaseOrder>

In po2.xml, all the elements in the instance belong to the same namespace, and the namespace statement declares a default namespace that applies to all the elements in the instance. Hence, it is unnecessary to explicitly prefix any of the elements. As another illustration of using qualified elements, the schemas in [Advanced Concepts III: The Quarterly Report] all require qualified elements.

Qualification of attributes is very similar to the qualification of elements. Attributes that must be qualified, either because they are declared globally or because the attributeFormDefault attribute is set to qualified, appear prefixed in instance documents. One example of a qualified attribute is the xsi:nil attribute that was introduced in [Nil Values]. In fact, attributes that are required to be qualified must be explicitly prefixed because the Namespaces in XML specification does not provide a mechanism for defaulting the namespaces of attributes. Attributes that are not required to be qualified appear in instance documents without prefixes, which is the typical case.

ref39The qualification mechanism we have described so far has controlled all local element and attribute declarations within a particular target namespace. It is also possible to control qualification on a declaration by declaration basis using the form attribute. For example, to require that the locally declared attribute publicKey is qualified in instances, we declare it in the following way:

NOTE: 

Requiring Qualification of Single Attribute

<schema xmlns="http://www.w3.org/2001/XMLSchema"
        xmlns:po="http://www.example.com/PO1"
        targetNamespace="http://www.example.com/PO1"
        elementFormDefault="qualified"
        attributeFormDefault="unqualified">
  <!-- etc. -->
  <element name="secure">
    <complexType>
      <sequence>
        <!-- element declarations -->
      </sequence>
      <attribute name="publicKey" type="base64Binary" form="qualified"/>
    </complexType>
  </element>
</schema>

Notice that the value of the form attribute overrides the value of the attributeFormDefault attribute for the publicKey attribute only. Also, the form attribute can be applied to an element declaration in the same manner. An instance document that conforms to the schema is:

NOTE: 

Instance with a Qualified Attribute

<?xml version="1.0"?>
<purchaseOrder xmlns="http://www.example.com/PO1"
               xmlns:po="http://www.example.com/PO1"
               orderDate="1999-10-20">
  <!-- etc. -->
  <secure po:publicKey="GpM7">
    <!-- etc. -->
  </secure>
</purchaseOrder>