Uniform Resource Name (URN)

Most people are familiar with URLs. With this character string, websites or other media on web servers, for example, can be assigned an address. Thanks to this iden­ti­fi­ca­tion, we are able access the world wide web. Yet there is also the URN, the Uniform Resource Name. Although def­i­nite­ly related to the Uniform Resource Locator, the URN has another important purpose. We’ll explain below what this is.

With a Uniform Resource Name, various items (resources) can be given a unique name. This is es­pe­cial­ly of interest on the internet, as there, different people and ap­pli­ca­tions encounter each other – and in doing so make exchanges related to specific objects. With a clear iden­ti­fi­er, you can be sure that all par­tic­i­pants are talking about the same content.

For this purpose, however, you must ensure that object iden­ti­fi­ca­tion functions reliably and does not change – that is to say, it is in­de­pen­dent of time and place. The URN is perfectly suited for guar­an­tee­ing this, as it is designed to be location-in­de­pen­dent and have no time limit. This means that even if you moves the data and stores it in another location, the name of the object won’t change.

The URN is rendered in URI syntax. Here the URN is provided with a specific scheme – the name for the first part of the syntax. This is followed by in­for­ma­tion that is separated by a colon.

Each URN thus consists of at least three parts.

• Each URN begins with the URN’s scheme spec­i­fi­ca­tion.
• Then the namespace iden­ti­fi­er (NID) follows, which must be reg­is­tered with IANA and (separated with ad­di­tion­al colons) can be sub­di­vid­ed.
• Finally, one finds the namespace-specific string (NSS), which then precisely iden­ti­fies the par­tic­u­lar object.

The namespace being used is managed by the Internet Assigned Numbers Authority (IANA). The official list contains more than 60 different name­spaces. The most well-known include:

• issn: In­ter­na­tion­al Standard Serial Number. A unique number for serials, such as pe­ri­od­i­cals.
• isbn: In­ter­na­tion­al Standard. Books Number. A unique iden­ti­fi­er for books.
• nbn: National Bib­li­og­ra­phy Number. A country-specific iden­ti­fi­ca­tion format for some national libraries.
• uuid: Uni­ver­sal­ly Unique Iden­ti­fi­er. A unique in­for­ma­tion iden­ti­fi­er within a computer system.
• isan: In­ter­na­tion­al Standard Au­dio­vi­su­al Number. A unique number for audio-visual works (e.g. movies) that is in­de­pen­dent of the release format.

The NBN serves as a good example. An URN with this namespace could for example look like this:

One can recognize in the iden­ti­fi­er that it is a matter of a URN being included in the NBN namespace. This however is specified further: With “de,” the country code (which stands for Germany - “Deutsch­land”) is es­tab­lished. A sub­name­space iden­ti­fi­er (SNID) then follows that denotes the German National Library. Only then does the iden­ti­fi­er of the actual work follow, with a long, unique number.

The Uniform Resource Names shares some sim­i­lar­i­ties with the Uniform Resource Locator (URL). Both the URN and URL are sub­cat­e­gories of the Uniform Resource Iden­ti­fi­er (URI). This iden­ti­fi­er was conceived so that every form of resource – re­gard­less of whether it is a website or email – can be iden­ti­fied and in­ter­act­ed with in a network such as the internet. This also applies to URL and URN; and in spite of their re­spec­tive par­tic­u­lar­i­ties, both sub­cat­e­gories follow the URI scheme.

However, URN and URL dif­fer­en­ti­ate them­selves in that the former per­ma­nent­ly iden­ti­fies a resource and the latter primarily specifies the path to the resource. While the URN is designed in such a way that the iden­ti­fi­er is in­de­pen­dent of where the data is stored, URLs point to a specific place where the resource is located. Both iden­ti­fi­er formats are thus similar to each other in their design, but serve different purposes.