Persistent Identifier
A persistent identifier (PID) is a long-lived, location-independent label for a digital or physical resource. PIDs power systems like DOI, ORCID, ROR, and Handle, replacing fragile URLs with strings that resolve to whatever location currently hosts the thing they name.
A persistent identifier (PID) is an identifier intended to remain stable over long periods of time, decoupled from the current location of the thing it identifies. The basic design pattern is indirection: instead of citing a URL that may rot, citers use a short opaque string that is resolved through a central service to the current canonical URL. When the underlying resource moves, only the resolver entry needs to change. PIDs are used for many classes of entity in research and culture. The Digital Object Identifier (DOI) names publications, datasets, and software via agencies such as Crossref and DataCite. Handle System provides the underlying resolver used by DOIs. ORCID identifies researchers; ROR identifies research organisations; ISBN and ISSN identify books and serials; ARK identifiers are used by libraries and archives; PURL provides a lightweight redirect-based PID; and URN is a generic IETF scheme. Good PID systems share several properties: a defined syntax, a governance body that guarantees the namespace, a resolver that can be operated independently of any one publisher, and metadata describing what the identifier refers to. They are not magic: a PID is only as persistent as the institutions and funding that maintain its resolver and the registrants who keep target URLs up to date. Dead DOIs and broken ORCID records are real, but at population scale PIDs dramatically reduce link rot compared to bare URLs.