Uniform Resource Name

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A Uniform Resource Name ( URN ; German "uniform name for resources") is a Uniform Resource Identifier (URI) with the scheme urnthat serves as a permanent, location-independent identifier for a resource . In other words, URNs are used to give resources unique and permanently valid names in order to be able to uniquely identify them. A resource can be anything that can somehow be clearly described - i.e. also very abstract or intangible things (such as a worldview, a concept or a measured radiation), but also concrete things such as a certain book.


URNs are URIs with the scheme urn. The schema-specific part of the URI is further subdivided into namespaces (NIDs, Namespace IDentifiers):

urn:<NID>:<NID-spezifischer Teil>

An example of this is the following URN


which clearly identifies the book “Modern Operating Systems” by Andrew S. Tanenbaum in the 2nd revised edition via its ISBN.

Some namespaces are divided into further sub-namespaces (e.g. urn:mpeg:mpeg7:schema:2001). The assignment of identifiers in a namespace or part of a namespace can be delegated here.

A URN can - depending on the namespace - either be a completely new identifier or an identifier such as an ISBN or ISSN that has already been assigned by other mechanisms.

The Internet Assigned Numbers Authority (IANA) provides a complete list of the defined namespaces in the network.

Example: German National Library

The German National Library provides the following models:

The following structure of URNs is common for libraries that belong to a library network :

urn: nbn: de: [Association abbreviation]: [ Library sigil ] - [unique number] [ check digit ]

Libraries / institutions / publishers outside the library networks usually generate URNs with the following structure:

urn: nbn: de: [four-digit numeric code] - [unique number] [check digit]

The German National Library's own sub-namespace is 101: 1 , URNs referring to it have the structure:

urn: nbn: de: 101: 1- [unique production number] [check digit]

“When delivering online publications that are subject to mandatory collection to the German National Library, the German National Library offers the assignment of urn: nbn: de as a persistent identifier as an additional service. In the delivery process, all incoming objects receive a URN. These URNs are usually assigned automatically by the German National Library itself from its own sub-namespace (urn: nbn: de: 101: 1). "

Use and comparison with urls

While URLs are intended to uniquely describe the place where a resource is located (to localize the resource), the purpose of URNs is to give the resource (and only this one) a globally unique name and thus make it accessible clearly identify their entire service life. Several URNs can be assigned to a resource.

A URN can be compared to a person's name , whereas a URL represents their address : A URN says who or what it is about, while a URL says where (at what location) the object (the resource) is located .

URNs and URLs can therefore complement each other: For example, one could say via an RFC : "The RFC urn: ietf: rfc: 3187 (URN) is located here: tools.ietf.org (URL)."

Since URNs (as opposed to URLs ) are independent of the location or other characteristics of the resource, a URN can be retained even if the location of a resource changes. Conversely, a new URN must be assigned to another resource, even if it is stored in the same location.

It is also conceivable that several logical resources and thus also several URNs are assigned to a physical resource. The 01/2004 edition of a journal (physical resource) could be available under the URN for the “current edition” as well as for the “special edition 01/2004” (which can be derived from an ISSN extension called SICI ).

Conversely, a URN can also be a collective name for several resources, e.g. For example, a URN (which could be derived from an ISSN) could designate all issues of a journal.


Since URNs (unlike URLs) identify a resource by clearly naming them , rather than by clearly describing where the resource is located , resources cannot be resolved using URNs as easily as, for example, URLs of DNS is the case. The Internet Engineering Task Force proposes the use of the Dynamic Delegation Discovery System (DDDS) for the resolution of URNs ( RFC 3401 , RFC 3402 , RFC 3404 , RFC 3405 ).

URNs cannot be called up directly. Rather, they first have to be translated into URLs or other URIs . These do not necessarily have to directly describe the resource you are looking for, but can also lead to metadata or sources of supply.

For example, it would be conceivable that when a user accesses a URN derived from an ISBN, they would not get to the full text of the book (which may not be available online), but instead to the catalog page of their preferred online bookstore (set in the browser ).

See also

Web links

Individual evidence

  1. Digital Item Declaration . In: mpeg.chiariglione.org . Moving Picture Experts Group (MPEG), accessed and received on July 31, 2017 (English).
  2. ^ Uniform Resource Names (URN) namespaces. IANA, May 3, 2017, accessed June 4, 2017 .
  3. a b Uta Ackermann, Christiane Berner, Natalie Elbert, Jürgen Kett, Kadir Karaca Koçer, Nicole von der Hude, Martina Wiegand: Policy for the assignment of URNs in the namespace urn: nbn: de . Version 1.0. In: d-nb.info . German National Library , November 29, 2012, urn: nbn: de: 101-2012121200 , accessed and received on July 31, 2017 (this policy replaces the EPICUR: Uniform Resource Name (URN) strategy of the German National Library ).
  4. Christa Schöning-Walter: The Uniform Resource Name (URN) . In: Heike Neuroth, Achim Oßwald, Regine Scheffel, S. Strathmann, Mathias Jehn (eds.): Nestor manual. A small encyclopedia of digital long-term archiving . Version 2.0. Verlag Werner Hülsbusch, Boizenburg 2009, ISBN 978-3-940317-48-3 , pp. Chapter 9: 46 – Chapter 9: 56, URN for Chapter 9.4.1 “The Uniform Resource Name (URN)” (Version 2.0 ): urn: nbn: de: 0008-20090811490 ( Chapter 9.4.1 "The Uniform Resource Name (URN)" (Version 2.0) as a PDF file (PDF) 858 KiB; collective work online ).
  5. BCP 66 (= RFC 3406 , 2002), Section 2.0: "A single resource, HOWEVER, may have more than one URN assigned to it for different purposes." - The German National Library requires contrast to its fund namespace -one correspondence ; see policy for the assignment of URNs in the namespace urn: nbn: de (2012), p. 7: "Each object can only be assigned one URN."