XML Pocket Reference, 3rd Edition

XML Namespaces

Namespaces provide a way to disambiguate names in XML documents, thus helping avoid a collision of names when multiple vocabularies are combined.

Examples

Default namespace declaration

<message xmlns="http://simonstl.com/ns/examples/message"
         xml:lang="en" date="20051006" >
   This is a message!
</message>

Qualified or prefixed namespace declaration

<msg:message xmlns:msg="http://simonstl.com/ns/examples/
message" xml:lang="en" date="20051006" >
   This is a message!
</msg:message>

Description

The special xmlns attribute, or xmlns with a prefix (for example, xmlns:xsl), specifies a namespace declaration.

Tip

Namespaces can be confusing because they can use any URI as a namespace name. The scheme or protocol name http:// suggests that the URI identifies a resource that can be retrieved just like any other web resource using Hypertext Transfer Protocol. But this is not the case. The URI is considered simply a name and is not a guarantee of the location or existence of a resource. URIs are allocated locally, so you don’t have to deal with a global registry in order to use them; however, the downside of this is you can’t really police people who might use a domain name you own as part of their URI.

Without a prefix, the xmlns attribute and its value (such as http://simonstl.com/ns/examples/message) are considered a default namespace declaration. A default namespace declaration associates a namespace name—a URI—with one or more elements; however, a default namespace declaration never