Uniform Resource Name
A Uniform Resource Name ( URN, engl. " Unified name for resource ") is a Uniform Resource Identifier ( URI) urn with the scheme that serves as a permanent, location-independent identifier for a resource. Stated differently URNs used to provide unique resources and permanently valid names to thus identify them unambiguously. A resource can be anything that can be described somehow clearly - including very abstract or intangible things ( such as a belief, a concept or a measured radiation ), but also concrete things such as a particular book.
URNs are URIs urn with the schema. The scheme - specific part of the URI is still in namespaces ( NIDs, namespace IDentifiers ) can be subdivided:
An example of this is the following URN
Which uniquely identifies the book " Modern Operating Systems" by Andrew S. Tanenbaum in the second revised edition of its ISBN.
Some namespaces are divided into further sub - namespaces ( eg urn: mpeg: MPEG7: schema: 2001). The assignment of identifiers in a namespace or part of a name space can hereby be delegated.
A URN can in this case - depending on the scope - either be a completely new identifier or an award already by other mechanisms such as an ISBN or ISSN identifiers.
For a complete list of defined namespaces is located under http://www.iana.org/assignments/urn-namespaces (English).
Example: German National Library
The German National Library are the following pattern before:
Libraries that belong to a library network, URNs structured along the following pattern
Institutions that do not fit into the organizational structure of the library networks such as publishers or in the case of a cooperative NBN award based not have in Germany, applied for at the German National Library its own sub-namespace. This is structured as a four digit number combination:
Your own archive is addressed:
Use and comparison with URLs
While URLs are meant to be the place where a resource is to clearly describe ( to locate the resource), it is the purpose of URNs to give the resource ( and only this ) a globally unique name and thus on their entire life to uniquely identify. A resource can thereby be assigned multiple URNs.
You can get a URN with the name of a person compare, whereas a URL is the address: A URN tells to whom or what it is, while a URL tells you where ( anywhere), the object ( the resource ) is.
URNs and URLs can therefore complement each other: You could say for example via a RFC: " The RFC urn: ietf: rfc: 3187 (URN ) is located here: http://tools.ietf.org/html/rfc3187.html ( URL). "
Since URNs (unlike URLs) are independent of the location or other characteristics of the resource, a URN can be maintained, even when changing the location of a resource. Conversely, another resource, a new URN to be assigned, even when it is stored at the same location.
Furthermore, it is conceivable that a physical resource multiple logical resources and therefore more URNs can be assigned. Thus, the output could 01 /2004 a magazine (physical resource) both under the URN for the " current issue " and for the " Special Edition 01/ 2004" (which may be derived from an ISSN extension called SICI ) must be available.
Conversely, a URN also be a collective name for several resources, such as might be a URN (which could be derived from an ISSN ) refer to all editions of a magazine.
Since URNs using (unlike URLs) identify a resource by the fact that they are clearly identified, and not the fact that they clearly describe where the resource is located, resources can not be so simply resolved based on URNs, as for example in URLs DNA of the case. The Internet Engineering Task Force proposes the use of the Dynamic Delegation Discovery System ( DDDS ) before ( RFC 3401, RFC 3402, RFC 3404, RFC 3405 ) for the resolution of URNs.
So URNs can not be called directly. Rather, they must first be translated into other URLs or URIs. These need not necessarily directly represent the resource you are looking, but can also lead to metadata or reference sources.
Thus, for example, conceivable that a user when calling a derived from an ISBN URN not to (possibly not available online) Full text of the book, but the alternative, come to the side of his catalog ( set in the browser ) favorite online bookstore.