 | Level: Intermediate Contributors: IETF 06 Feb 2007
Updated 25 Apr 2007 Uniform Resource Identifiers (URIs) define a standard
system for identifying resources on the Web, including HTML pages, XML
documents, images, multimedia files, and more. Get to know how URIs,
Uniform Resource Names (URNs), and URLs are related, discover the
difference between absolute and relative URIs, and learn about
Internationalized Resource Identifiers (IRIs), an enhanced version of
URIs with better support for non-English speakers.
Uniform Resource Identifiers (URIs) are the standard
mechanism for identifying resources on the Web, governed by RFC 3986: Uniform Resource
Identifier Generic Syntax [IETF RFC]. A URI is an extension of the
familiar URLs used in Web browsers and the like. All URLs are also URIs,
but URIs also include URNs, governed by
RFC 2141: Uniform Resource
Names
[IETF RFC]. URNs are a way to identify Web resources by
name rather than location. URIs are generally used in XML core
specifications as system identifiers, which specify a concrete
resource, such as a file, referenced from an XML document. In XML, the
concept of absolute and relative URIs is extremely important. If you
imagine browsing the Web and that the current Web page is the starting
point for a request for the next page, an absolute URI identifies the
same new resource regardless of the starting point, while a relative URI
identifies a new resource that depends on the starting point.
RFC 3987:
Internationalized Resource Identifiers (IRIs) [IETF RFC] are just
like URIs except that they can use the whole range of Unicode
characters. URIs are limited to the ASCII subset of characters -- only
127 characters based on the needs of English-speaking users -- and this
causes much difficulty for non-English users. An IRI has a standard
encoding as a URI, in case you need to use it in a protocol (such as
HTTP) that accepts only URIs.
Resources
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