urnNIDNSS

urnNIDNSS is an informal shorthand used to describe the two main components of a Uniform Resource Name (URN): the Namespace Identifier (NID) and the Namespace-Specific String (NSS). A URN is structured as urn:<NID>:<NSS>, where the NID identifies the namespace and the NSS specifies the resource within that namespace. The exact rules for the NSS are defined by the namespace’s own specification, while the NID itself must be registered and governed according to IETF/IANA processes.

In practice, urnNIDNSS embodies the idea that a URN is a persistent, location-independent name, with the NID indicating which namespace governs the resource and the NSS providing the resource’s identifier within that namespace. NIDs are registered in the IANA URN Namespace Registry and are accompanied by namespace-specific definitions that determine allowed characters, encoding, and any structural constraints for the NSS. The NSS may be a simple numeric string or a more complex string with hyphens, colons, or other permitted characters, often requiring percent-encoding for certain characters depending on the namespace rules.

Examples commonly cited include urn:isbn:0451450523 for an ISBN, urn:uuid:123e4567-e89b-12d3-a456-426614174000 for a UUID-based URN, and urn:issn:1535-3613 for an ISSN. While URNs provide a framework for persistent naming, not all URNs are universally resolvable to a dereferenceable resource; resolution typically depends on dedicated resolvers or namespace-specific infrastructure.