XML in a Nutshell, 3rd Edition

Target Namespaces

Associating a schema with a particular XML namespace is extremely simple: add a targetNamespace attribute to the root xs:schema element, like so:

<xs:schema xmlns:xsi="http://www.w3.org/2001/XMLSchema"
  targetNamespace="http://namespaces.oreilly.com/xmlnut/address">

Tip

It is important to remember that many XML 1.0 documents are not associated with namespaces at all. To validate these documents, it is necessary to use a schema that doesn’t have a targetNamespace attribute. When developing schemas that are not associated with a target namespace, you should always explicitly qualify schema elements (like xs:element) to keep them from being confused with global declarations for your application.

However, making that simple change impacts numerous other parts of the example application. Trying to validate the addressdoc.xml document as it stands (with the xsi:noNamespaceSchemaLocation attribute) causes the Xerces schema processor to report this validity error:

General Schema Error: Schema in address-schema.xsd has a different target 
namespace from the one specified in the instance document :.

To rectify this, it is necessary to change the instance document to reference the new, namespace-enabled schema properly. This is done using the xsi:schemaLocation attribute, like so:

<fullName xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://namespaces.oreilly.com/xmlnut/address 
    address-schema.xsd"
  language="en">Scott Means</fullName>

Notice that ...