Uniform Resource Identifier: Difference between revisions

Revision as of 05:48, 14 May 2025

Revision as of 23:14, 14 May 2025

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=== 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=W3C |date= 1992-02-24 February 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 [[Internet 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 |publisher=Corporation for National Research Initiatives |date=July 1992 |website=IETF|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 |publisher=Corporation for National Research Initiatives |date=November 1992 |website=IETF |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 ===

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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.

The [[Semantic Web]] uses the HTTP URI scheme to identify both documents and concepts for practical uses, a distinction which has caused confusion as to how to distinguish the two. The ''TAG'' published an e-mail in 2005 with a solution of the problem, which became known as the ''httpRange-14 resolution''.<ref>{{cite web |last1=Fielding |first1=Roy |title=[httpRange-14] Resolved |url=https://lists.w3.org/Archives/Public/www-tag/2005Jun/0039.html |website=W3C Public mailing list archives |access-date=6 December 2020 |date=18 JunJune 2005}}</ref> The W3C subsequently published an Interest Group Note titled "Cool URIs for the Semantic Web", which explained the use of [[content negotiation]] and the [[HTTP 303]] response code for redirections in more detail.<ref>{{cite web |editor-last1=Sauermann |editor-first1=Leo |editor-first2=Richard |editor-last2=Cyganiak |first1= Danny |last1=Ayers |first2=Max |last2=Völkel |title=Cool URIs for the Semantic Web |url=https://www.w3.org/TR/cooluris/ |website=W3C |access-date=6 December 2020 |date=3 December 3, 2008}}</ref>

== Design ==

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A URI has a scheme that refers to a specification for assigning identifiers within that scheme. As such, the URI syntax is a federated and extensible naming system wherein each scheme's specification may further restrict the syntax and semantics of identifiers using that scheme. The URI generic syntax is a superset of the syntax of all URI schemes. It was first defined in {{IETF RFC|2396}}, published in August 1998,{{Ref RFC|2396}} and finalized in {{IETF RFC|3986}}, published in January 2005.{{Sfn|Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry|2005|p=46|ps=; "9. Acknowledgements"}}

A URI is composed from an allowed set of [[ASCII]] characters consisting of [[Filename|reserved characters]] (gen-delims: <code>:</code>, <code>/</code>, <code>?</code>, <code>#</code>, <code>[</code>, <code>]</code>, and <code>@</code>; sub-delims: <code>!</code>, <code>$</code>, <code>&</code>, <code>'</code>, <code>(</code>, <code>)</code>, <code>*</code>, <code>+</code>, <code>,</code>, <code>;</code>, and <code>=</code>),{{Sfn|Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry|2005|ps=; "2.2. Reserved Characters", "2.3. Unreserved Characters"|pp=13-1413–14}} unreserved characters ([[Latin-script alphabet|uppercase and lowercase letters]], [[Arabic numerals|decimal digits]], <code>-</code>, <code>.</code>, <code>_</code>, and <code>~</code>),{{Sfn|Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry|2005|ps=; "2.2. Reserved Characters", "2.3. Unreserved Characters"|pp=13-1413–14}} and the character <code>%</code>.{{Sfn|Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry|2005|ps=; "2.1. Percent-Encoding"|pp=12}} Syntax components and subcomponents are separated by ''delimiters'' from the reserved characters (only from generic reserved characters for components) and define ''identifying data'' represented as unreserved characters, reserved characters that do not act as delimiters in the component and subcomponent respectively,{{Ref RFC|3986|rsection=2}} and [[percent-encoding]]s when the corresponding character is outside the allowed set or is being used as a delimiter of, or within, the component. A percent-encoding of an identifying data [[Octet (computing)|octet]] is a sequence of three characters, consisting of the character <code>%</code> followed by the two hexadecimal digits representing that octet's numeric value.{{Ref RFC|3986|rsection=2.1}}

<section begin="syntax"/><!-- This section is transcluded in other articles. See Help:Labeled section transclusion -->The URI generic syntax consists of five ''components'' organized hierarchically in order of decreasing significance from left to right:{{Ref RFC|3986|rsection=3}}

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=== Works cited ===

* {{cite IETF|last=[[Tim Berners-Lee|Berners-Lee, Tim]]; [[Roy Fielding|Fielding, Roy T.]]; [[Larry Masinter|Masinter, Larry]] |rfc=3986 |title=RFC 3986 Uniform Resource Identifier (URI): Generic Syntax |date=January 2005 |publisher=Internet Engineering Task Force |language=en |access-date=16 February 2024-02-16 }}

== Further reading ==

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{{refbegin|32em}}

* {{cite book |author-first=Elliotte Rusty |author-last=Harold |author-link=Elliotte Rusty Harold |date=2004 |title=XML 1.1 Bible |edition=Third |publisher=[[Wiley Publishing]] |page=291 |isbn=978-0-7645-4986-1}}

* {{cite IETF|rfc=7595 |title=Guidelines and Registration Procedures for URI Schemes |editor-first=Dave |editor-last=Thaler |author-first1=Tony |author-last1=Hansen |author-first2=Ted |author-last2=Hardie |journal=IETF Request for Comments (RFC) Pages -– Test |publisher=[[Internet Engineering Task Force]] |date=June 2015 |issn=2070-1721 |ref={{SfnRef|IETF|2015}}}}

* {{cite book |author-last=Morrison |author-first=Michael Wayne |author-link=Michael Wayne Morrison |date=2006 |title=Sams Teach Yourself XML |publisher=[[Sams Publishing]] |chapter=Hour 5: ''Putting Namespaces to Use'' |page=91}}

* {{cite web |author=((URI Planning Interest Group, W3C/IETF)) |title=URIs, URLs, and URNs: Clarifications and Recommendations 1.0 |url=http://www.w3.org/TR/uri-clarification/ |date=21 September 2001 |access-date=2009-07-27 July 2009 |ref={{SfnRef|URI Planning Interest Group|2009}}}}

* {{cite web |url=http://www.w3.org/2001/tag/doc/alternatives-discovery.html |title=On Linking Alternative Representations To Enable Discovery And Publishing |publisher=[[World Wide Web Consortium]] |date=2006 |orig-year=2001 |access-date=3 April 2012-04-03 |ref={{SfnRef|W3C|2001}}}}

* {{cite web |url=http://www.w3.org/TR/REC-xml-names/#iri-use |title=Namespaces in XML 1.1 (Second Edition) |date=16 August 2006 |at=2.2 Use of URIs as Namespace Names |editor-first1=Tim |editor-last1=Bray |editor-link1=Tim Bray |editor-first2=Dave |editor-last2=Hollander |editor-first3=Andrew |editor-last3=Layman |editor-first4=Richard |editor-last4=Tobin |publisher=[[World Wide Web Consortium]] |access-date=31 August 2015 |ref={{SfnRef|W3C|2006}}}}

* {{cite web |url=http://www.w3.org/TR/cooluris/ |title=Cool URIs for the Semantic Web |editor-first1=Leo |editor-last1=Sauermann |editor-first2=Richard |editor-last2=Cyganiak |author-first1=Danny |author-last1=Ayers |author-first2=Max |author-last2=Völkel |publisher=[[World Wide Web Consortium]] |date=3 December 2008 |access-date=3 April 2012-04-03 |ref={{SfnRef|W3C|2008}}}}

* {{cite web |url=http://www.w3.org/TR/REC-xml-names/#iri-use |title=Namespaces in XML 1.0 (Third Edition) |date=8 December 2009 |at=2.2 Use of URIs as Namespace Names |editor-first1=Tim |editor-last1=Bray |editor-link1=Tim Bray |editor-first2=Dave |editor-last2=Hollander |editor-first3=Andrew |editor-last3=Layman |editor-first4=Richard |editor-last4=Tobin |editor-first5=Henry S. |editor-last5=Thompson |publisher=[[World Wide Web Consortium]] |access-date=31 August 2015 |ref={{SfnRef|W3C|2009}}}}

* {{cite IETF|rfc=1866|section=8.2.1 |title=Hypertext Markup Language – 2.0 |author-first1=Tim |author-last1=Berners-Lee |author-link1=Tim Berners-Lee |author-first2=Daniel "Dan" |author-last2=Connolly |author-link2=Daniel Connolly (computer scientist) |publisher=[[Internet Engineering Task Force]] |date=November 1995 |s2cid=6628570 |access-date=13 September 2015 |ref={{SfnRef|RFC 1866|1995}} }}

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* {{cite IETF |title=Uniform Resource Identifiers (URI): Generic Syntax |rfc=3986 |author-first1=Tim |author-last1=Berners-Lee |author-link1=Tim Berners-Lee |author-first2=Roy T. |author-last2=Fielding |author-link2=Roy T. Fielding |author-first3=Larry |author-last3=Masinter |author-link3=Larry Masinter |publisher=[[Internet Engineering Task Force]] |date=January 2005 |access-date=31 August 2015 |ref={{SfnRef|RFC 3986|2005}}}}

* {{cite IETF |rfc=3986|section=3 |title=Uniform Resource Identifiers (URI): Generic Syntax|sectionname=Syntax Components |author-first1=Tim |author-last1=Berners-Lee |author-link1=Tim Berners-Lee |author-first2=Roy T. |author-last2=Fielding |author-link2=Roy T. Fielding |author-first3=Larry |author-last3=Masinter |author-link3=Larry Masinter |publisher=[[Internet Engineering Task Force]] |date=January 2005 |access-date=31 August 2015 |ref={{SfnRef|RFC 3986, section 3|2005}}}}

* {{cite web |author-last1=Lawrence |author-first1=Eric |title=Browser Arcana: IP Literals in URLs |url=http://blogs.msdn.com/b/ieinternals/archive/2014/03/06/browser-arcana-ipv4-ipv6-literal-urls-dotted-va-dotless.aspx |website=IEInternals |publisher=[[Microsoft]] |date=6 March 2014 |access-date=2016-04-25 April 2016}}

{{refend}}

* {{cite journal|journal=[[IEEE Internet Computing]]|year=1998|doi= 10.1109/4236.722228|issn=1941-0131|volume=2|issue=5|title=WebDAV: IEFT standard for collaborative authoring on the Web|first=E.J|last=Whitehead|pages=34–40 |url=https://ieeexplore.ieee.org/document/722228|access-date=12 October 2021}}