2.5. Using Namespaces
The Java language uses packages to avoid name clashes. Programmers can use the same name for different classes as long as they aren’t in the same package. XML has a similar namespace mechanism for element and attribute names.
A namespace is identified by a Uniform Resource Identifier (URI), such as
http://www.w3.org/2001/XMLSchema uuid:1c759aed-b748-475c-ab68-10679700c4f2 urn:com:books-r-us
The HTTP URL form is the most common. Note that the URL is just used as an identifier string, not as a locator for a document. For example, the namespace identifiers
denote different namespaces, even though a web server would serve the same document for both ...