URN: The Uniform Resource Name Explained
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.
What is the URN?
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.
Although it’s true that various resource types can theoretically be addressed via URN, in practice one primarily uses the format for media. In libraries especially, URNs have been established in order to be able to clearly identify books and other content. In doing so, additional information can be utilized, such as ISBNs.
The Structure of a URN
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.
URN, URL and URI: The Differences Explained
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.