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UR* Terms

The basic picture, specified in section 1.2. URI, URL, and URN of RFC 2396, looks like this:

         _______________________________________________________
        |         ________________                              |
        |        |  ftp:          |                             |
        |        |  gopher:       |                             |
        |        |  http:       __|____________                 |
        |        |  etc        |  |  urn:      |                |
        |        |_____________|__|            |                |
        |                URLs  |               |                |
        |                      |_______________|                |
        |                             URNs                      |
        |_______________________________________________________|
                               URIs

URI

Uniform Resource Identifier. The generic set of all names/addresses that are short strings that refer to resources.

URL

Uniform Resource Locator. An informal term (no longer used in technical specifications) associated with popular URI schemes: http, ftp, mailto, etc.

URN

Uniform Resource Name.

1. An URI that has an institutional commitment to persistence, availability, etc. Note that this sort of URI may also be a URL. See, for example, PURLs.
2. A particular scheme, urn:, specified by RFC2141 and related documents, intended to serve as persistent, location-independent, resource identifiers.

See also: an index of web architecture terms, a glossary of web terms.