A URN (Uniform Resource Name) is an Internet resource with a name that has a persistent significance – that is, one (or a software) can expect to always find the resource. A common problem on Web is that Web contents are sometime moved to a new site or a new page on the same site and since links are made using Uniform Resource Locators (URLs), they no longer work as the contents are moved.
A URN is something like a URL. For example, below is a hypothetical URN:
Here “def://” indicates an agency or an accessible directory of all dictionaries, glossaries, and encyclopedias on the Internet and “ip address” the name of a term. The result of using the agency could be the “best definition,” the “longest definition,” or even all definitions that the agency could find of “ip address.”
A URL whereas would need to specify one specific location for that definition such as:
Here the user must know where the resource is located along with the exact spell of the file name and suffix. With URN, the user only needs to know the name of the resource. One or more agencies will presumably be able to locate the nearest copy of the resource and the user need not remember where resources are located or relocated to.
Both URN and URL are types of a concept – the Uniform Resource Identifier (URI). A URN is associated with a concept called Uniform Resource Characteristics (URC), which allows descriptive information to be associated with a URN, such as author, date, length, etc.