Name and Addresses: URL, URN, URI, URC

Names and Addresses: URL, URN, URI, URC

The key to distributed network processing is publishing and locating named objects. A heirarchy of naming conventions have been proposed as a standard for the Web.

A Uniform Resource Locator (URL) provides a non-persistent means to uniquely identify an object within a namespace. The format is: transport://user:password@host:port/path.
A Uniform Resource Name (URN) provides persistent names within a namespace. This would allow a permanent object to be mirrored over several known sites; if one were unavailable, the object could be found/resolved at another site. Several proposals for URNs exist; none have been widely adopted, yet.
Uniform Resource Identifier (URI) is an abstraction that includes both URLs and URNs. This is the standard addressing mechanism for the Web.
A Uniform Resource Citation (URC) provides a set of attribute/value pairs used to describe URIs: authorship, publishers, copyright, etc. No proposed standard has been submitted yet.

URL Specification - RFC1738

URN Draft - PATH proposal

URI Specification - RFC1630

Other References

World Wide Web Consortium