URI

Uniform Resource Identifiers

Uniform Resource Identifiers (URIs, aka URLs) are short strings that identify resources in the web: documents, images, downloadable files, services, electronic mailboxes, and other resources. They make resources available under a variety of naming schemes and access methods such as HTTP, FTP, and Internet mail addressable in the same simple way. They reduce the tedium of "log in to this server, then issue this magic command ..." down to a single click.

It is an extensible technology: there are a number of existing addressing schemes, and more may be incorporated over time.

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 <a href="http://www.ietf.org/rfc/rfc2141.txt">RFC2141 and related documents, intended to serve as persistent, location-independent, resource identifiers.

Articles:

• A Beginner's Guide to URLs
• Cool URLs Don't Change
• The classic intro to URLs, by The NCSA Mosaic team