XML.com FAQs > D. Developers and Implementors (including WebMasters and server operators)
Question:  D.5 What's a namespace?

Randall Fowle writes: A namespace is a collection of element and attribute names identified by a Uniform Resource Identifier reference. The reference appears in the root element as a value of the xmlns attribute. For example, the namespace reference for an XML document with a root element x might appear like this: <x xmlns="http://www.company.com/company-schema">.

More than one namespace may appear in a single XML document, to allow a name to be used more than once. Each reference can declare a prefix to be used by each name, so the previous example might appear as <x xmlns:spc="http://www.company.com/company-schema">, which would nominate the namespace for the `spc' prefix: <spc:name>Mr. Big</spc:name>.

The reference does not need to be a physical file; it is simply a way to distinguish between namespaces. The reference should tell a person looking at the XML document where to find definitions of the element and attribute names using that particular namespace.

This FAQ is from The XML FAQ, maintained by Peter Flynn