What is the URN?
With a « Uniform Resource Name », a persistent identifier specifically designed by the Internet Engineering Task Force (IETF), various items or resources can be given a unique name.
This is especially of interest on the Internet where different people and applications encounter each other – and in doing so make exchanges related to specific objects. Thanks to an unambiguous identifier, one can make sure that all stakeholders are referring to the same content.
URN, URL and URI: the logical relationships
The Uniform Resource Name (URN) shares some similarities with the well-known « Uniform Resource Locator » (URL).
Both the URN and URL are subcategories of the Uniform Resource Identifier. This overarching identifier was designed so that every form of resource (files of any kind, entities…) can be identified and interacted with in a network such as the Internet.
However, URN and URL have major differences:
– the URN permanently identifies a resource,
– the URL primarily specifies the path to the resource, which may change over time, for two reasons. First, the resource available in a given URL location may change. This content drift is all too common on the Internet. Second, the resource may move to a different location, and it can be available in multiple locations at the same time. Thus URLs are often neither unique nor persistent.
Both URLs and URNs are thus similar to each other in their design, but serve different purposes.
URN has been designed to be interoperable with existing standard identifier systems like ISSN (and also with any kind of standardized new system). This is the reason why it has identifier system specific namespaces, unlike other persistent identifier systems (for instance the DOI prefix does not indicate an identifier system, but an organization which assigns identifiers). URL (and URI) do not take traditional identifier systems into account at all. So the URN for a serial is based on the ISSN of the serial, and in the URN:ISSN namespace ISSN rules are applied. In contrast, the URL of the homepage of a serial usually has nothing to do with the ISSN.
The Structure of a URN
The URN is rendered in URI syntax.
Each URN thus consists of at least three parts.
– URN: Each URN begins with the URN’s scheme specification.
– NID: it is the namespace identifier which is registered with IANA (Internet Assigned Numbers Authority).
– NSS: it is the namespace-specific string (NSS), which then precisely identifies the particular object.
The ISSN as a URN
The ISSN was one of the very first bibliographic identifiers to adopt the URN scheme so as to be used and expressed in a standardized way over the Web.
Each ISSN can thus be expressed as a URN through the following syntax:
(where xxxx-xxxx is the specific ISSN being translated as a URN)
It is recommended to record the URN:ISSN in the embedded metadata of the resource made available on the web, e.g. a journal published on the web. For example, in an HTML document, it should be entered in the HEAD section as follows:
• META NAME=”Identifier” SCHEME=”URN:ISSN” CONTENT=”1234-1231″
Resolution of «URN:ISSN»
URNs can be used not only as « internet identifiers » but also as « actionable pointers » allowing machines or humans to retrieve the identified resources, or relevant metadata describing them, through a resolution mechanism, i.e. a « resolver ».
The ISSN International Centre provides such a resolver for «URN:ISSN » (https://urn.issn.org). The syntax to be used to retrieve the metadata corresponding to an ISSN through this resolver is:
(where xxxx-xxxx is the ISSN being targeted)
This request will retrieve the corresponding ISSN record made accessible through the ISSN Portal, together with the URL(s) (if any) pointing to the resource.
Internet Engineering Task Force (IETF) Reference Documents
Namespace Registration for International Standard Serial Number (ISSN) and Linking ISSN (ISSN-L) based on ISO 3297:2007
(Revision of the earlier registration RFC 3044)
RFC 8254 : Uniform Resource Names (URNs)
(Complete information about URNs and URN namespace registration processes)
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