URIs must be used for the prefix names. A URI (Uniform Resource Identifier) is a string of characters that identifies a resource. It can be URL (Uniform Resource Locator) or URN (Universal Resource Name). The URL we're using is simply used as a name, for the namespace. XML parser won't try to pull back any resources from that location. XML parser uses it for naming the namespaces in the document.
Book List
xmlns:pub="http://www.rntsoft.com/namespaces/pub"> Mastering XHTML Ed Tittel
Java Developer’s Guide to E-Commerce with XML and JSP William Brogden