Uniform Resource Identifier: Difference between revisions

Revision as of 23:57, 17 August 2024

Revision as of 03:14, 25 August 2024

Line 21:

A '''Uniform Resource Identifier''' ('''URI'''), formerly '''Universal Resource Identifier''', is a unique sequence of characters that identifies an abstract or physical resource,{{Sfn|Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry|2005|p=1|ps=, "Abstract"}} such as resources on a webpage, mail address, phone number,{{Sfn|Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry|2005|p=7|ps=; "1.1.2. Examples", "1.1.3. URI, URL, and URN"}} books, real-world objects such as people and places, concepts.{{Sfn|Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry|2005|p=5|ps=, "Resource: the term "resource" is used in a general sense for whatever might be identified by a URI"}} URIs are used to identify anything described using the [[Resource Description Framework]] (RDF), for example, concepts that are part of an [[Ontology (information science)|ontology]] defined using the [[Web Ontology Language]] (OWL), and people who are described using the [[FOAF (ontology)|Friend of a Friend vocabulary]] would each have an individual URI.

URIs which provide a means of locating and [[Information retrieval|retrieving]] information resources on a network (either on the Internet or on another private network, such as a computer filesystem or an [[Intranet]]) are [[Uniform Resource Locator]]s ('''URLs'''). Therefore, URLs are a subset of URIs, ie. every URL is a URI (and not necessarily the other way around).{{Sfn|Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry|2005|p=7|ps=; "1.1.2. Examples", "1.1.3. URI, URL, and URN"}} Other URIs provide only a unique name, without a means of locating or retrieving the resource or information about it; these are [[Uniform Resource Name]]s (URNs). The web technologies that use URIs are not limited to [[Web browser|web browsers]].

== History ==

Line 27:

=== Conception ===

URIs and URLs have a shared history. In 1990, [[Tim Berners-Lee]]|Tim Berners-Lee's]] proposals for [[hypertext]] implicitly introduced the idea of a URL as a short string representing a resource that is the target of a [[hyperlink]].<ref>{{cite web |last1=Palmer |first1=Sean |title=The Early History of HTML |url=http://infomesh.net/html/history/early/ |website=infomesh.net |access-date=6 December 2020}}</ref> At the time, people referred to it as a "hypertext name"<ref>{{cite web |title=W3 Naming Schemes |url=https://www.w3.org/History/19921103-hypertext/hypertext/WWW/Addressing/Addressing.html |website=www.w3.org |date=1992 |access-date=6 December 2020}}</ref> or "document name".

Over the next three and a half years, as the [[World Wide Web|World Wide Web's]] core technologies of [[HTML]], [[HTTP]], and [[Web browser|web browsers]] developed, a need to distinguish a string that provided an address for a resource from a string that merely named a resource emerged. Although not yet formally defined, the term ''Uniform Resource Locator'' came to represent the former, and the more contentious ''Uniform Resource Name'' came to represent the latter. In July 1992 Berners-Lee's report on the [[IETFInternet Engineering Task Force]] (IETF) "UDI (Universal Document Identifiers) [[Birds of a feather (computing)|BOF]]" mentions URLs (as Uniform Resource Locators), URNs (originally, as Unique Resource Numbers), and the need to charter a new working group.<ref>{{cite web |title=Proceedings of the Twenty-Fourth Internet Engineering Task Force |page=193 |url=https://www.ietf.org/proceedings/24.pdf |access-date=27 July 2021}}</ref> In November 1992 the IETF "URI Working Group" met for the first time.<ref>{{cite web |title=Proceedings of the Twenty-Fifth Internet Engineering Task Force |page=501 |url=https://www.ietf.org/proceedings/25.pdf |access-date=27 July 2021}}</ref>

During the debate over defining URLs and URNs, it became evident that the concepts embodied by the two terms were merely aspects of the fundamental, overarching, notion of resource ''identification''. In June 1994, the [[IETF]] published Berners-Lee's first ''Request for Comments'' that acknowledged the existence of URLs and URNs. Most importantly, it defined a formal syntax for ''Universal Resource Identifiers'' (i.e. URL-like strings whose precise syntaxes and semantics depended on their schemes). In addition, the {{IETF RFC|1630}} attempted to summarize the syntaxes of URL schemes in use at the time. It acknowledged -- ''but did not standardize''—the existence of relative URLs and fragment identifiers.{{Ref RFC|1630}}

=== Refinement ===

Line 37:

In December 1994, {{IETF RFC|1738}} formally defined relative and absolute URLs, refined the general URL syntax, defined how to resolve relative URLs to absolute form, and better enumerated the URL schemes then in use.{{Ref RFC|1738}} The agreed definition and syntax of URNs had to wait until the publication of IETF {{IETF RFC|2141}}{{Ref RFC|2141}} in May 1997.

The publication of IETF {{IETF RFC|2396}}{{Ref RFC|2396}} in August 1998 saw the URI syntax become a separate specification{{Ref RFC|2396}} and most of the parts of RFCs 1630 and 1738 relating to URIs and URLs in general were revised and expanded by the [[IETF]]. The new RFC changed the meaning of ''U'' in ''URI'' from "Universal" to "Uniform."

In December 1999, {{IETF RFC|2732}}{{Ref RFC|2732}} provided a minor update to <nowiki>RFC 2396</nowiki>, allowing URIs to accommodate [[IPv6]] addresses. A number of shortcomings discovered in the two specifications led to a community effort, coordinated by <nowiki>RFC 2396</nowiki> co-author [[Roy Fielding]], that culminated in the publication of IETF {{IETF RFC|3986}}{{Ref RFC|3986}} in January 2005. While obsoleting the prior standard, it did not render the details of existing URL schemes obsolete; <nowiki>RFC 1738</nowiki> continues to govern such schemes except where otherwise superseded. IETF {{IETF RFC|2616}}{{Ref RFC|2616}} for example, refines the <code>http</code> scheme. Simultaneously, the IETF published the content of <nowiki>RFC 3986</nowiki> as the full standard STD 66, reflecting the establishment of the URI generic syntax as an official Internet protocol.

In 2001, the W3C[[World Wide Web Consortium|World Wide Web Consortium's]] (W3C) Technical Architecture Group (TAG) published a guide to [[best practices]] and canonical URIs for publishing multiple versions of a given resource.<ref>{{cite web |last1=Raman |first1=T.V. |title=On Linking Alternative Representations To Enable Discovery And Publishing |url=https://www.w3.org/2001/tag/doc/alternatives-discovery.html |website=www.w3.org |access-date=6 December 2020 |date=1 November 2006}}</ref> For example, content might differ by language or by size to adjust for capacity or settings of the device used to access that content.

In August 2002, IETF {{IETF RFC|3305}}{{Ref RFC|3305}} pointed out that the term "URL" had, despite widespread public use, faded into near obsolescence, and serves only as a reminder that some URIs act as addresses by having schemes implying network accessibility, regardless of any such actual use. As URI-based standards such as [[Resource Description Framework]] make evident, resource identification need not suggest the retrieval of resource representations over the Internet, nor need they imply network-based resources at all.

Line 57:

A URN is analogous to a person's name, while a URL is analogous to their street address. In other words, a URN identifies an item and a URL provides a method for finding it.

Technical publications, especially standards produced by the [[Internet Engineering Task Force|IETF]] and by the [[World Wide Web Consortium|W3C]], normally reflect a view outlined in a [[W3C Recommendation]] of 30 July 2001, which acknowledges the precedence of the term URI rather than endorsing any formal subdivision into URL and URN. {{cquote|URL is a useful but informal concept: a URL is a type of URI that identifies a resource via a representation of its primary access mechanism (e.g., its network "___location"), rather than by some other attributes it may have.<ref>{{cite web |last1=((URI Planning Interest Group, W3C/IETF)) |title=URIs, URLs, and URNs: Clarifications and Recommendations 1.0 |url=https://www.w3.org/TR/uri-clarification/ |website=www.w3.org |publisher=W3C/IETF |access-date=8 December 2020 |date=September 2001}}</ref>}}

As such, a URL is simply a URI that happens to point to a resource over a network.{{efn|A report published in 2002 by a joint W3C/IETF working group aimed to normalize the divergent views held within the IETF and W3C over the relationship between the various 'UR*' terms and standards. While not published as a full standard by either organization, it has become the basis for the above common understanding and has informed many standards since then.}}{{Ref RFC|3305}} However, in non-technical contexts and in software for the World Wide Web, the term "URL" remains widely used. Additionally, the term "web address" (which has no formal definition) often occurs in non-technical publications as a synonym for a URI that uses the ''http'' or ''https'' schemes. Such assumptions can lead to confusion, for example, in the case of XML namespaces that have a [[#Relation to XML namespaces|visual similarity to resolvable URIs]].