Web and XML Glossary

The WWW is considered to include objects accessed using an extendable number of Protocols, existing, invented for the WWW itself, or to be invented in the future. Access instructions for an individual object under a given Protocol are encoded into forms of address string. Other Protocols allow the use of object names of various forms. In order to abstract the idea of a generic object, the WWW needs the concepts of the universal set of objects, and of the universal set of names or addresses of objects. A URI is a member of this universal set of names in registered name spaces and addresses referring to registered Protocols or name spaces. A URL is a form of URI which expresses an address mapping onto an access Algorithm using network Protocols. A URN is a form of URI which uses a name space (and associated Resolution Protocols) for persistent object names.