Uniform Resource Name

<h2 id="uris-urns-and-urls">URIs, URNs, and URLs</h2>
URNs were originally conceived to be part of a three-part <a href="/facts/Information_architecture/xhAHVzA7">information architecture</a> for the Internet, along with <a href="/facts/Uniform_Resource_Locator/pPD5g7Wq">Uniform Resource Locators (URLs)</a> and <a href="/facts/Uniform_Resource_Characteristic/WRoWBwvG">Uniform Resource Characteristics (URCs)</a>, a <a href="/facts/Metadata/qt35z79C">metadata</a> framework. As described in <a href="/facts/RFC_(identifier)/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc1737">1737</a>,<a class="footnote-ref" id="fnref:2" href="#fn:2">2</a> and later in RFC <a href="https://datatracker.ietf.org/doc/html/rfc2141">2141</a>,<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a> URNs were distinguished from URLs, which identify resources by specifying their locations in the context of a particular access protocol, such as <a href="/facts/HTTP/TWtvf7JD">HTTP</a> or <a href="/facts/FTP/THuWgzfw">FTP</a>. In contrast, URNs were conceived as <a href="/facts/Persistent_identifier/hsPK2mkQ">persistent</a>, location-independent identifiers assigned within defined <a href="/facts/Namespace/9efXwMtV">namespaces</a>, typically by an authority responsible for the namespace, so that they are globally unique and persistent over long periods of time, even after the resource which they identify ceases to exist or becomes unavailable.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a> 
URCs never progressed past the conceptual stage,<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> and other technologies such as the <a href="/facts/Resource_Description_Framework/WMufyukm">Resource Description Framework</a> later took their place. Since RFC <a href="https://datatracker.ietf.org/doc/html/rfc3986">3986</a><a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> in 2005, use of the terms "Uniform Resource Name" and "Uniform Resource Locator" has been deprecated in technical standards in favor of the term Uniform Resource Identifier (URI), which encompasses both, a view proposed in 2001 by a joint working group between the <a href="/facts/World_Wide_Web_Consortium/lGWmhF6M">World Wide Web Consortium</a> (W3C) and <a href="/facts/Internet_Engineering_Task_Force/tIcCsFhX">Internet Engineering Task Force</a> (IETF).<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>
A URI is a <a href="/facts/Character_string_(computer_science)/4ChJu5WS">string</a> of <a href="/facts/Character_(computing)/X2zKLFFB">characters</a> used to <a href="/facts/Identifier/pPaQPLhj">identify</a> or <a href="/facts/Name/b0E3kuD1">name</a> a <a href="/facts/Web_resource/42wbl7QV">resource</a> on the internet. URIs are used in many Internet protocols to refer to and access information resources. URI schemes include the http and ftp protocols, as well as hundreds of others.
In the "contemporary view", as it is called, all URIs identify or name resources, perhaps uniquely and persistently, with some of them also being "locators" which are resolvable in conjunction with a specified protocol to a representation of the resources.
Other URIs are not locators and are not necessarily resolvable within the bounds of the systems where they are found. These URIs may serve as names or identifiers of resources. Since resources can move, opaque identifiers which are not locators and are not bound to particular locations are arguably more likely than identifiers which are locators to remain unique and persistent over time. But whether a URI is resolvable depends on many operational and practical details, irrespective of whether it is called a "name" or a "locator". In the contemporary view, there is no bright line between "names" and "locators".
In accord with this way of thinking, the distinction between Uniform Resource Names and Uniform Resource Locators is now no longer used in formal <a href="/facts/Internet_Engineering_Task_Force/tIcCsFhX">Internet Engineering Task Force</a> technical standards, though the latter term, URL, is still in wide informal use.
The term "URN" continues now as one of more than a hundred URI "schemes", urn:, paralleling http:, ftp:, and so forth. URIs of the urn: scheme are not locators, are not required to be associated with a particular protocol or access method, and need not be resolvable. They should be assigned by a procedure which provides some assurance that they will remain unique and identify the same resource persistently over a prolonged period. Some namespaces under the urn: scheme, such as <a href="/facts/UUID/SUtkYJPe">urn:uuid:</a> assign identifiers in a manner which does not require a registration authority, but most of them do. A typical URN namespace is <a href="/facts/ISBN/15AdSPa9">urn:isbn</a>, for International Standard Book Numbers. This view is continued in RFC <a href="https://datatracker.ietf.org/doc/html/rfc8141">8141</a> (2017).<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a>
There are other URI schemes, such as <a href="/facts/Tag_URI_scheme/smtFGrJd">tag:</a>, <a href="/facts/Info_URI_scheme/3Q8n4xnh">info:</a> (now largely deprecated), and ni:<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> which are similar to the urn: scheme in not being locators and not being associated with particular resolution or access protocols.

<h2 id="syntax">Syntax</h2>
The syntax of a urn: scheme URI is represented in the <a href="/facts/Augmented_Backus%E2%80%93Naur_form/coNbJGD2">augmented Backus–Naur form</a> as:<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a><a class="footnote-ref" id="fnref:11" href="#fn:11">11</a>

namestring = assigned-name
 [ rq-components ]
 [ "#" f-component ]
assigned-name = "urn" ":" NID ":" NSS
NID = (alphanum) 0*30(ldh) (alphanum)
ldh = alphanum / "-"
NSS = pchar *(pchar / "/")
rq-components = [ "?+" r-component ]
 [ "?=" q-component ]
r-component = pchar *( pchar / "/" / "?" )
q-component = pchar *( pchar / "/" / "?" )
f-component = fragment

; general URI syntax rules (RFC3986)
fragment      = *( pchar / "/" / "?" )
pchar         = unreserved / pct-encoded / sub-delims / ":" / "@"
pct-encoded   = "%" HEXDIG HEXDIG
unreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~"
sub-delims    = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="

alphanum      = ALPHA / DIGIT  ; obsolete, usage is deprecated

or, in the form of a <a href="/facts/Syntax_diagram/NdvSrCKb">syntax diagram</a>, as:

<ul><li>The leading scheme (urn:) is case-insensitive.</li>
<li><NID> is the namespace identifier, and may include letters, digits, and -.</li>
<li>The NID is followed by the namespace-specific string <NSS>, the interpretation of which depends on the specified namespace. The NSS may contain ASCII letters and digits, and many punctuation and special characters. Disallowed ASCII and <a href="/facts/Unicode/DDu3MfPV">Unicode</a> characters may be included if <a href="/facts/Percent-encoded/zprLw5se">percent-encoded</a>.</li></ul>
In 2017, the syntax for URNs was updated:<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>

<ul><li>The slash character (/) is now allowed in the NSS to represent names containing slashes from non-URN identifier systems.</li>
<li>The q-component was added to enable passing of parameters to named resources.</li>
<li>The r-component was added to enable passing of parameters to resolvers. However, the updated specification notes that it should not be used until its semantics are defined via further standardization.</li></ul>
<h2 id="namespaces">Namespaces</h2>
In order to ensure the global uniqueness of URN namespaces, their identifiers (NIDs) are required to be registered with the <a href="/facts/Internet_Assigned_Numbers_Authority/b6MlP6zQ">IANA</a>. Registered namespaces may be "formal" or "informal". An exception to the registration requirement was formerly made for "experimental namespaces",<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> since rescinded by RFC 8141.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>

<h3>Formal</h3>
Approximately sixty formal URN namespace identifiers have been registered. These are namespaces where Internet users are expected to benefit from their publication,<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a> and are subject to several restrictions. They must:

<ul><li>Not be an already-registered NID</li>
<li>Not start with urn-</li>
<li>Be more than two letters long</li>
<li>Not start with XY-, where XY is any combination of two <a href="/facts/ASCII/vGUI33Qu">ASCII</a> letters</li>
<li>Not start with x- (see "Experimental namespaces", below)</li></ul>
<h3>Informal</h3>
Informal namespaces are registered with IANA and assigned a number sequence (chosen by IANA on a first-come-first-served basis) as an identifier,<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a> in the format

"urn-" ⟨number⟩
Informal namespaces are fully fledged URN namespaces and can be registered in global registration services.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>

<h3>Experimental</h3>
An exception to the registration requirement was formerly made for "experimental namespaces".<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a> However, following the deprecation of the "X-" notation for new identifier names,<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a> RFC <a href="https://datatracker.ietf.org/doc/html/rfc8141">8141</a><a class="footnote-ref" id="fnref:20" href="#fn:20">20</a> did away with experimental URN namespaces, indicating a preference for use of the <a href="urn:example">urn:example</a> namespace where appropriate.<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a>

<h2 id="examples">Examples</h2>
<table><tbody><tr><th>URN</th><th>corresponds to</th></tr><tr><td>urn:isbn:0451450523</td><td>The 1968 book <a href="/facts/The_Last_Unicorn/n5vmS7bL">The Last Unicorn</a>, identified by its <a href="/facts/ISBN/15AdSPa9">International Standard Book Number</a>.</td></tr><tr><td>urn:isan:0000-0000-2CEA-0000-1-0000-0000-Y</td><td>The 2002 film <a href="/facts/Spider-Man_(2002_film)/SL1shgAY">Spider-Man</a>, identified by its <a href="/facts/International_Standard_Audiovisual_Number/r71z8WVI">International Standard Audiovisual Number</a>.</td></tr><tr><td>urn:ISSN:0167-6423</td><td>The scientific journal Science of Computer Programming, identified by its <a href="/facts/International_Standard_Serial_Number/DPAflDvU">International Standard Serial Number</a>.</td></tr><tr><td>urn:ietf:rfc:2648</td><td>The <a href="/facts/IETF/tIcCsFhX">IETF</a>'s RFC 2648.</td></tr><tr><td>urn:mpeg:mpeg7:schema:2001</td><td>The default namespace rules for <a href="/facts/MPEG-7/LzPlxytB">MPEG-7</a> video metadata.</td></tr><tr><td>urn:oid:2.16.840</td><td>The <a href="/facts/Object_identifier/wEC9ubWd">OID</a> for the <a href="/facts/United_States/P0sCdLe5">United States</a>.</td></tr><tr><td>urn:uuid:6e8bc430-9c3a-11d9-9669-0800200c9a66</td><td>A version 1 <a href="/facts/Universally_unique_identifier/SUtkYJPe">UUID</a>.</td></tr><tr><td>urn:nbn:de:bvb:19-146642</td><td>A <a href="/facts/National_Bibliography_Number/2VlG0lEc">National Bibliography Number</a> for a document, indicating country (<a href="/facts/ISO_3166-2:DE/kCIkm36M">de</a>), regional network (bvb = <a href="/facts/Bibliotheksverbund_Bayern/4P6hhgV8">Bibliotheksverbund Bayern</a>), library number (19) and document number.</td></tr><tr><td>urn:lex:eu:council:directive:2010-03-09;2010-19-UE</td><td>A <a href="/facts/Directive_(European_Union)/KS076mKR">directive of the European Union</a>, using the proposed <a href="/facts/Lex_(URN)/a8XUsbAb">Lex URN namespace</a>.</td></tr><tr><td>urn:lsid:zoobank.org:pub:CDC8D258-8F57-41DC-B560-247E17D3DC8C</td><td>A <a href="/facts/LSID/BRBxrHqp">Life Science Identifiers</a> that may be resolved to <a href="http://zoobank.org/urn:lsid:zoobank.org:pub:CDC8D258-8F57-41DC-B560-247E17D3DC8C">http://zoobank.org/urn:lsid:zoobank.org:pub:CDC8D258-8F57-41DC-B560-247E17D3DC8C</a> .</td></tr><tr><td>urn:epc:class:lgtin:4012345.012345.998877</td><td><a href="/facts/Global_Trade_Item_Number/NKewx6Bj">Global Trade Item Number</a> with lot/batch number. As defined by Tag Data Standard<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a> (TDS). See more examples at <a href="/facts/Electronic_Product_Code/7nrjMF1A">EPC Identification Keys</a>.</td></tr><tr><td>urn:epc:id:sgtin:0614141.112345.400</td><td><a href="/facts/Global_Trade_Item_Number/NKewx6Bj">Global Trade Item Number</a> with an individual serial number</td></tr><tr><td>urn:epc:id:sscc:0614141.1234567890</td><td><a href="/facts/Serial_Shipping_Container_Code/mlJoqPIn">Serial Shipping Container Code</a></td></tr><tr><td>urn:epc:id:sgln:0614141.12345.400</td><td><a href="/facts/Global_Location_Number/vgmUouwK">Global Location Number</a> with extension</td></tr><tr><td>urn:epc:id:bic:CSQU3054383</td><td>BIC <a href="/facts/Intermodal_container/797lTKzR">Intermodal container</a> Code as per <a href="/facts/ISO_6346/ASoCRkwr">ISO 6346</a></td></tr><tr><td>urn:epc:id:imovn:9176187</td><td><a href="/facts/IMO_number/5rQ1jxju">IMO Vessel Number</a> of marine vessels</td></tr><tr><td>urn:epc:id:gdti:0614141.12345.400</td><td><a href="/facts/Global_Document_Type_Identifier/hSSt73Gp">Global Document Type Identifier</a> of a document instance</td></tr><tr><td>urn:mrn:iala:aton:us:1234.5</td><td>Identifier for <a href="https://www.iala-aism.org/product/g1143-unique-identifiers-for-maritime-resources-2/">Marine Aids to Navigation</a></td></tr><tr><td>urn:mrn:iala:vts:ca:ecareg</td><td>Identifier for Vessel Traffic Services</td></tr><tr><td>urn:mrn:iala:wwy:us:atl:chba:potri</td><td>Identifier for <a href="https://www.iala-aism.org/product/g1143-unique-identifiers-for-maritime-resources-2/">Waterways</a></td></tr><tr><td>urn:mrn:iala:pub:g1143</td><td>Identifier for <a href="https://www.iala-aism.org/">IALA</a> publications</td></tr><tr><td>urn:microsoft:adfs:claimsxray</td><td>Identifier for federated identity; this example is from Claims X-Ray<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a></td></tr><tr><td>urn:eic:10X1001A1001A450</td><td><a href="/facts/European_Network_of_Transmission_System_Operators_for_Electricity/ReLlmkwd">European Network of Transmission System Operators for Electricity</a> (ENTSO-E), identified by its <a href="/facts/Energy_Identification_Code/M07gh55w">Energy Identification Code</a></td></tr></tbody></table>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Archival_Resource_Key/KAk6MVuI">Archival Resource Key</a> (ARK)</li>
<li><a href="/facts/.arpa/8NemUcEU">.arpa</a> – urn.arpa is for dynamic discovery</li>
<li><a href="/facts/Extensible_resource_identifier/Jnzr81NX">Extensible resource identifier</a> (XRI)</li>
<li><a href="/facts/Handle_System/rdebSxmC">Handle System</a></li>
<li><a href="/facts/Info_URI_scheme/3Q8n4xnh">Info URI scheme</a></li>
<li><a href="/facts/LSID/BRBxrHqp">Life Science Identifiers</a> (LSID)</li>
<li>The <a href="/facts/Magnet_URI_scheme/dGRRYeXM">Magnet URI scheme</a>, which uses URNs</li>
<li><a href="/facts/Persistent_Uniform_Resource_Locator/KKYhANhT">Persistent Uniform Resource Locator</a> (PURL)</li>
<li><a href="/facts/Tag_URI_scheme/smtFGrJd">Tag URI scheme</a> is like urn: in its URIs not being resource locators</li>
<li><a href="/facts/Digital_Object_Identifier/muM9Etpq">Digital Object Identifier</a> (DOI)</li>
<li><a href="/facts/Electronic_Product_Code/7nrjMF1A">EPC Identification Keys</a>.</li>
<li><a href="https://www.iala-aism.org/technical/data-modelling/mrn/">Maritime Resource Names (MRN)</a></li></ul>

<h3>Citations</h3>

<h3>Sources</h3>

<ul><li>K. Sollins; <a href="/facts/Larry_Masinter/GuKjgjhB">L. Masinter</a> (December 1994). <a href="https://datatracker.ietf.org/doc/html/rfc1737">Functional Requirements for Uniform Resource Names</a>. Network Working Group. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC1737">10.17487/RFC1737</a>. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc1737">1737</a>. Informational.</li>
<li>R. Moats (May 1997). <a href="/facts/Paul_Vixie/wsagrYzy">P. Vixie</a> (ed.). <a href="https://datatracker.ietf.org/doc/html/rfc2141">URN Syntax</a>. Network Working Group. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC2141">10.17487/RFC2141</a>. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc2141">2141</a>. Proposed Standard. Obsoleted by RFC <a href="https://datatracker.ietf.org/doc/html/rfc8141">8141</a>.</li>
<li>L. Daigle; D.W. van Gulik; R. Iannella; P. Faltstrom (October 2002). <a href="https://datatracker.ietf.org/doc/html/rfc3406">Uniform Resource Names (URN) Namespace Definition Mechanisms</a>. Network Working Group. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC3406">10.17487/RFC3406</a>. BCP 66. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc3406">3406</a>. Best Current Practice 66. Obsoleted by RFC <a href="https://datatracker.ietf.org/doc/html/rfc8141">8141</a>. Obsoletes RFC <a href="https://datatracker.ietf.org/doc/html/rfc2611">2611</a>.</li>
<li><a href="/facts/Tim_Berners-Lee/JRv21mt9">T. Berners-Lee</a>; <a href="/facts/Roy_Fielding/Arp1Qy5X">R. Fielding</a>; <a href="/facts/Larry_Masinter/GuKjgjhB">L. Masinter</a> (January 2005). <a href="https://datatracker.ietf.org/doc/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</a>. Network Working Group. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC3986">10.17487/RFC3986</a>. STD 66. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc3986">3986</a>. Internet Standard 66. Obsoletes RFC <a href="https://datatracker.ietf.org/doc/html/rfc2732">2732</a>, <a href="https://datatracker.ietf.org/doc/html/rfc2396">2396</a> and <a href="https://datatracker.ietf.org/doc/html/rfc1808">1808</a>. Updated by RFC <a href="https://datatracker.ietf.org/doc/html/rfc6874">6874</a>, <a href="https://datatracker.ietf.org/doc/html/rfc7320">7320</a> and <a href="https://datatracker.ietf.org/doc/html/rfc8820">8820</a>. Updates RFC <a href="https://datatracker.ietf.org/doc/html/rfc1738">1738</a>.</li>
<li>P. Saint-Andre; D. Crocker; M. Nottingham (June 2012). <a href="https://datatracker.ietf.org/doc/html/rfc6648">Deprecating the "X-" Prefix and Similar Constructs in Application Protocols</a>. <a href="/facts/Internet_Engineering_Task_Force/tIcCsFhX">Internet Engineering Task Force</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC6648">10.17487/RFC6648</a>. <a href="/facts/ISSN_(identifier)/DPAflDvU">ISSN</a> <a href="https://search.worldcat.org/issn/2070-1721">2070-1721</a>. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc6648">6648</a>. Best Current Practice.</li>
<li>S. Farrell; D. Kutscher; C. Dannewitz; B. Ohlman; A. Keranen; P. Hallam-Baker (April 2013). <a href="https://datatracker.ietf.org/doc/html/rfc6920">Naming Things with Hashes</a>. <a href="/facts/Internet_Engineering_Task_Force/tIcCsFhX">Internet Engineering Task Force</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC6920">10.17487/RFC6920</a>. <a href="/facts/ISSN_(identifier)/DPAflDvU">ISSN</a> <a href="https://search.worldcat.org/issn/2070-1721">2070-1721</a>. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc6920">6920</a>. Proposed Standard.</li>
<li>P. Saint-Andre (May 2013). <a href="https://datatracker.ietf.org/doc/html/rfc6963">A Uniform Resource Name (URN) Namespace for Examples</a>. <a href="/facts/Internet_Engineering_Task_Force/tIcCsFhX">Internet Engineering Task Force</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC6963">10.17487/RFC6963</a>. <a href="/facts/ISSN_(identifier)/DPAflDvU">ISSN</a> <a href="https://search.worldcat.org/issn/2070-1721">2070-1721</a>. BCP 183. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc6963">6963</a>. Best Current Practice 183. Updates RFC <a href="https://datatracker.ietf.org/doc/html/rfc1930">1930</a>.</li>
<li>P. Saint-Andre; <a href="/facts/John_C._Klensin/vKFykDm2">J. Klensin</a> (April 2017). <a href="https://datatracker.ietf.org/doc/html/rfc8141">Uniform Resource Names (URNs)</a>. <a href="/facts/Internet_Engineering_Task_Force/tIcCsFhX">Internet Engineering Task Force</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC8141">10.17487/RFC8141</a>. <a href="/facts/ISSN_(identifier)/DPAflDvU">ISSN</a> <a href="https://search.worldcat.org/issn/2070-1721">2070-1721</a>. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc8141">8141</a>. Proposed Standard. Obsoletes RFC <a href="https://datatracker.ietf.org/doc/html/rfc2141">2141</a>, <a href="https://datatracker.ietf.org/doc/html/rfc3406">3406</a>.
<ul><li>P. Saint-Andre; <a href="/facts/John_C._Klensin/vKFykDm2">J. Klensin</a> (April 2017). <a href="https://datatracker.ietf.org/doc/html/rfc8141">Uniform Resource Names (URNs)</a>. <a href="/facts/Internet_Engineering_Task_Force/tIcCsFhX">Internet Engineering Task Force</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.17487%2FRFC8141">10.17487/RFC8141</a>. <a href="/facts/ISSN_(identifier)/DPAflDvU">ISSN</a> <a href="https://search.worldcat.org/issn/2070-1721">2070-1721</a>. <a href="/facts/Request_for_Comments/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc8141">8141</a>. Proposed Standard. sec. 2. Obsoletes RFC <a href="https://datatracker.ietf.org/doc/html/rfc2141">2141</a>, <a href="https://datatracker.ietf.org/doc/html/rfc3406">3406</a>. § 2. URN Syntax</li></ul></li>
<li><a href="https://www.doi.org/factsheets/DOIIdentifierSpecs.html">"Factsheet: DOI System and Internet Identifier Specifications"</a>. International DOI Foundation. October 2012. Retrieved 2012-12-06.</li>
<li>W3C/IETF URI Planning Interest Group (21 September 2001). <a href="https://www.w3.org/TR/uri-clarification/">"URIs, URLs, and URNs: Clarifications and Recommendations 1.0"</a>. <a href="/facts/W3C/lGWmhF6M">W3C</a>. Retrieved 2012-12-07.{{cite web}}: CS1 maint: numeric names: authors list (link)</li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://www.iana.org/assignments/urn-namespaces/">Official IANA Registry of URN Namespaces</a></li>
<li><a href="http://datatracker.ietf.org/wg/urn/charter/">Uniform Resource Names working group</a> at the IETF</li>
<li><a href="http://www.benmeadowcroft.com/webdev/articles/urns-and-citations/">URNs and bibliographic citations in web authoring</a></li>
<li>An example server-side URN resolver is described in <a href="/facts/RFC_(identifier)/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc2169">2169</a>.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">RFC 8141 (2017). <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">RFC 1737 (1994). <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">RFC 2141 (1997). <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">RFC 8141 (2017). <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">W3C/IETF (2001). - W3C/IETF URI Planning Interest Group (21 September 2001). "URIs, URLs, and URNs: Clarifications and Recommendations 1.0". W3C. Retrieved 2012-12-07. <a href="https://www.w3.org/TR/uri-clarification/" target="_blank">https://www.w3.org/TR/uri-clarification/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">RFC 3986 (2005). <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">W3C/IETF (2001). - W3C/IETF URI Planning Interest Group (21 September 2001). "URIs, URLs, and URNs: Clarifications and Recommendations 1.0". W3C. Retrieved 2012-12-07. <a href="https://www.w3.org/TR/uri-clarification/" target="_blank">https://www.w3.org/TR/uri-clarification/</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">RFC 8141 (2017). <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">RFC 6920 (2013). <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">RFC 3986 (2005). <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">RFC 8141, section 2 (2017). <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">RFC 8141 (2017). <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">RFC 3406 (2002). <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">RFC 8141 (2017). <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">RFC 8141 (2017). <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">RFC 8141 (2017). <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">RFC 8141 (2017). <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">RFC 3406 (2002). <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">RFC 6648 (2012). <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">RFC 8141 (2017). <a href="#fnref:20" class="footnote-back-ref">↩</a></li>
<li id="fn:21">RFC 6963 (2013). <a href="#fnref:21" class="footnote-back-ref">↩</a></li>
<li id="fn:22">"EPC Tag Data Standard, version 1.13". GS1. Nov 2019. Retrieved 7 March 2021. <a href="https://www.gs1.org/standards/epcrfid-epcis-id-keys/epc-rfid-tds/1-13" target="_blank">https://www.gs1.org/standards/epcrfid-epcis-id-keys/epc-rfid-tds/1-13</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></li>
<li id="fn:23">"Claims X-Ray AD FS Help". <a href="https://adfshelp.microsoft.com/ClaimsXray/TokenRequest" target="_blank">https://adfshelp.microsoft.com/ClaimsXray/TokenRequest</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></li>
</ol>

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