urns

URNs, or Uniform Resource Names, are a type of Uniform Resource Identifier (URI) designed to serve as persistent, location-independent identifiers for resources. Unlike URLs, which point to a resource’s current location, URNs are intended to remain valid even if the resource moves or changes its location. They are used to provide stable references in contexts such as bibliographic records, standards documents, and library catalogs.

A URN has the form urn:<NID>:<NSS>, where the prefix urn: identifies the identifier as a URN. The namespace identifier (NID) specifies the namespace, such as isbn for books or doi for digital objects, and the namespace-specific string (NSS) is defined by that namespace. The governance of each namespace is handled by registries that publish the allowed values and the rules for the NSS.

Resolution and dereferencing of URNs are not universal; they depend on the namespace. Some namespaces provide resolution services or registries that map the URN to a location or metadata. For example, urn:doi:10.1000/182 can be resolved through a DOI resolver, and a related web redirect can be obtained via services like https://doi.org/10.1000/182 or through a bridge like https://n2t.net/urn:doi:10.1000/182. Not all URNs have a global dereferencing mechanism, and some are primarily used as stable identifiers within controlled systems.

URNs are standardized within the broader URI framework, with current guidance in RFCs such as RFC 8141. They are commonly used for persistent identifiers in scholarly publishing, library catalogs, and standards bodies, where long-term stability and unchanging references are important. See also Uniform Resource Identifier, DOI, ISBN, and URL.