UniformResourceIdentifiers

http://www.ietf.org/rfc/rfc2369.txt ([[RFC]])

웹에서 리소스들을 구별하기 위한 간단한 문자열. 이것을 이용하여 문서와 다운로드할 파일들, 이미지들, 서비스들, 그리고 다른 공유된 정보의 리소스들을 구별한다.

예를들어
 * file : file://usr/bin/python
 * [[FTP]] : ftp://somehost/somefile
 * [[HTTP]] : http://somehost/somefile
 * [[SMTP]] : mailto:someone@someaddress.com
 * [[Telnet]] : telnet://somehost

인터넷에서 논리적인 이름으로 영구정보를 식별하는데 [[URN]]을 사용한다.

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. 
  1. A particular scheme, urn:, specified by RFC2141 and related documents, intended to serve as persistent, location-independent, resource identifiers.