AUniform Resource Name (URN) is aUniform Resource Identifier (URI) that uses theurnscheme. URNs are globally uniquepersistent identifiers assigned within definednamespaces so they will be available for a long period of time, even after the resource which they identify ceases to exist or becomes unavailable.[1] URNs cannot be used to directly locate an item and need not be resolvable, as they are simply templates that another parser may use to find an item.
URNs were originally conceived to be part of a three-partinformation architecture for the Internet, along withUniform Resource Locators (URLs) andUniform Resource Characteristics (URCs), ametadata framework. As described inRFC 1737,[2] and later inRFC 2141,[3] URNs were distinguished from URLs, which identify resources by specifying their locations in the context of a particular access protocol, such asHTTP orFTP. In contrast, URNs were conceived aspersistent, location-independent identifiers assigned within definednamespaces, 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.[1]
URCs never progressed past the conceptual stage,[4] and other technologies such as theResource Description Framework later took their place. SinceRFC 3986[5] 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 theWorld Wide Web Consortium (W3C) andInternet Engineering Task Force (IETF).[4]
A URI is astring ofcharacters used toidentify orname aresource on the internet. URIs are used in many Internet protocols to refer to and access information resources. URI schemes include thehttp andftp 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 whichare not locators and are not bound to particular locations are arguably more likely than identifiers whichare 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 ResourceNames and Uniform ResourceLocators is now no longer used in formalInternet Engineering Task Force 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:, parallelinghttp:,ftp:, and so forth. URIs of theurn: 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 theurn: scheme, such asurn:uuid: assign identifiers in a manner which does not require a registration authority, but most of them do. A typical URN namespace isurn:isbn, for International Standard Book Numbers. This view is continued inRFC 8141 (2017).[1]
There are other URI schemes, such astag:,info: (now largely deprecated), andni:[6] which are similar to theurn: scheme in not being locators and not being associated with particular resolution or access protocols.
The syntax of aurn: scheme URI is represented in theaugmented Backus–Naur form as:[5][7]
namestring=assigned-name[rq-components]["#"f-component]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="%"HEXDIGHEXDIGunreserved=ALPHA/DIGIT/"-"/"."/"_"/"~"sub-delims="!"/"$"/"&"/"'"/"("/")"/"*"/"+"/","/";"/"="alphanum=ALPHA/DIGIT; obsolete, usage is deprecated
or, in the form of asyntax diagram, as:
urn:) is case-insensitive.<NID> is the namespace identifier, and may include letters, digits, and-.<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 andUnicode characters may be included ifpercent-encoded.In 2017, the syntax for URNs was updated:[1]
/) is now allowed in the NSS to represent names containing slashes from non-URN identifier systems.In order to ensure the global uniqueness of URN namespaces, their identifiers (NIDs) are required to be registered with theIANA. Registered namespaces may be "formal" or "informal". An exception to the registration requirement was formerly made for "experimental namespaces",[8] since rescinded by RFC 8141.[1]
Approximately sixty formal URN namespace identifiers have been registered. These are namespaces where Internet users are expected to benefit from their publication,[1] and are subject to several restrictions. They must:
urn-XY-, where XY is any combination of twoASCII lettersx- (see "Experimental namespaces", below)Informal namespaces are registered with IANA and assigned a number sequence (chosen by IANA on a first-come-first-served basis) as an identifier,[1] in the format
"urn-"⟨number⟩Informal namespaces are fully fledged URN namespaces and can be registered in global registration services.[1]
An exception to the registration requirement was formerly made for "experimental namespaces".[8] However, following the deprecation of the "X-" notation for new identifier names,[9]RFC 8141[1] did away with experimental URN namespaces, indicating a preference for use of theurn:example namespace where appropriate.[10]
| URN | corresponds to |
|---|---|
urn:isbn:0451450523 | The 1968 bookThe Last Unicorn, identified by itsInternational Standard Book Number. |
urn:isan:0000-0000-2CEA-0000-1-0000-0000-Y | The 2002 filmSpider-Man, identified by itsInternational Standard Audiovisual Number. |
urn:ISSN:0167-6423 | The scientific journalScience of Computer Programming, identified by itsInternational Standard Serial Number. |
urn:ietf:rfc:2648 | TheIETF's RFC 2648. |
urn:mpeg:mpeg7:schema:2001 | The default namespace rules forMPEG-7 video metadata. |
urn:oid:2.16.840 | TheOID for theUnited States. |
urn:uuid:6e8bc430-9c3a-11d9-9669-0800200c9a66 | A version 1UUID. |
urn:nbn:de:bvb:19-146642 | ANational Bibliography Number for a document, indicating country (de), regional network (bvb =Bibliotheksverbund Bayern), library number (19) and document number. |
urn:lex:eu:council:directive:2010-03-09;2010-19-UE | Adirective of the European Union, using the proposedLex URN namespace. |
urn:lsid:zoobank.org:pub:CDC8D258-8F57-41DC-B560-247E17D3DC8C | ALife Science Identifiers that may be resolved tohttp://zoobank.org/urn:lsid:zoobank.org:pub:CDC8D258-8F57-41DC-B560-247E17D3DC8C[permanent dead link] . |
urn:epc:class:lgtin:4012345.012345.998877 | Global Trade Item Number with lot/batch number. As defined by Tag Data Standard[11] (TDS). See more examples atEPC Identification Keys. |
urn:epc:id:sgtin:0614141.112345.400 | Global Trade Item Number with an individual serial number |
urn:epc:id:sscc:0614141.1234567890 | Serial Shipping Container Code |
urn:epc:id:sgln:0614141.12345.400 | Global Location Number with extension |
urn:epc:id:bic:CSQU3054383 | BICIntermodal container Code as perISO 6346 |
urn:epc:id:imovn:9176187 | IMO Vessel Number of marine vessels |
urn:epc:id:gdti:0614141.12345.400 | Global Document Type Identifier of a document instance |
urn:mrn:iala:aton:us:1234.5 | Identifier forMarine Aids to Navigation |
urn:mrn:iala:vts:ca:ecareg | Identifier forVessel Traffic Services |
urn:mrn:iala:wwy:us:atl:chba:potri | Identifier forWaterways |
urn:mrn:iala:pub:g1143 | Identifier forIALA publications |
urn:microsoft:adfs:claimsxray | Identifier for federated identity; this example is from Claims X-Ray[12] |
urn:eic:10X1001A1001A450 | European Network of Transmission System Operators for Electricity (ENTSO-E), identified by itsEnergy Identification Code |
§ 2. URN Syntax
| International | |
|---|---|
| National | |
