In contrast, URNs were conceived as persistent, location-independent identifiers assigned within defined namespaces, typically by an authority responsible for the namespace, so that they are globally unique and persistent over long periods of time, even after the resource which they identify ceases to exist or becomes unavailable.
[1] URCs never progressed past the conceptual stage,[4] and other technologies such as the Resource Description Framework later took their place.
Since RFC 3986[5] in 2005, use of the terms "Uniform Resource Name" and "Uniform Resource Locator" has been deprecated in technical standards in favor of the term Uniform Resource Identifier (URI), which encompasses both, a view proposed in 2001 by a joint working group between the World Wide Web Consortium (W3C) and Internet Engineering Task Force (IETF).
But whether a URI is resolvable depends on many operational and practical details, irrespective of whether it is called a "name" or a "locator".
In accord with this way of thinking, the distinction between Uniform Resource Names and Uniform Resource Locators is now no longer used in formal Internet Engineering Task Force technical standards, though the latter term, URL, is still in wide informal use.
URIs of the urn: scheme are not locators, are not required to be associated with a particular protocol or access method, and need not be resolvable.
They should be assigned by a procedure which provides some assurance that they will remain unique and identify the same resource persistently over a prolonged period.