XML Namespaces

XML namespaces provide a simple method for qualifying element and attribute names used in Extensible Markup Language documents by associating them with namespaces identified by URI references.  An XML namespace is a collection of names, identified by a URI reference  which is used in XML documents as element types and attributes. 

Applications of Extensible Markup Language (XML) where a single XML document may contain elements and attributes (here referred to as a "markup vocabulary") may be defined for and used by multiple software modules. One motivation for this is modularity; if such a markup vocabulary exists which is well-understood and for which there is useful software available, it is better to re-use this markup rather than re-invent it.

Such documents, containing multiple markup vocabularies, pose problems of recognition and collision. Software modules need to be able to recognize the tags and attributes which they are designed to process, even in the face of "collisions" occurring when markup intended for some other software package uses the same element type or attribute name.

These considerations require that document constructs should have universal names, whose scope extends beyond their containing document. This specification describes a mechanism,  XML namespaces, which accomplishes this.

Note:  XML namespaces differ from the "namespaces" conventionally used in computing disciplines in that the XML version has internal structure and is not, mathematically speaking, a set.