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.