A persistent identifier (PI or PID) is a long-lasting reference to a document, file, web page, or other object. The term "persistent identifier" is usually used in the context of digital objects that are accessible over the Internet. Typically, such an identifier is not only persistent but actionable: you can plug it into a web browser and be taken to the identified source. Of course, the issue of persistent identification predates the Internet. Over centuries, writers and scholars developed standards for

citation A citation is a reference to a source. More precisely, a citation is an abbreviated alphanumeric expression embedded in the body of an intellectual work that denotes an entry in the bibliographic references section of the work for the purpose o ...

of paper-based documents so that readers could reliably and efficiently find a source that a writer mentioned in a footnote or bibliography. After the Internet started to become an important source of information in the 1990s, the issue of citation standards became important in the online world as well. Studies have shown that within a few years of being cited, a significant percentage of web addresses go "dead", a process often called

link rot Link rot (also called link death, link breaking, or reference rot) is the phenomenon of hyperlinks tending over time to cease to point to their originally targeted file, web page, or server due to that resource being relocated to a new address ...

. Using a persistent identifier can slow or stop this process. An important aspect of persistent identifiers is that "persistence is purely a matter of service". That means that persistent identifiers are only persistent to the degree that someone commits to resolving them for users. No identifier can be inherently persistent, however many persistent identifiers are created within institutionally administered systems with the aim to maximise longevity. However, some regular

URLs A Uniform Resource Locator (URL), colloquially termed as a web address, is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identi ...

(i.e. web addresses), maintained by the website owner, are intended to be long-lasting; these are often called

permalink A permalink or permanent link is a URL that is intended to remain unchanged for many years into the future, yielding a hyperlink that is less susceptible to link rot. Permalinks are often rendered simply, that is, as clean URLs, to be easier to ...

Examples

People and organisations: * Open Researcher and Contributor ID (ORCID) *

Research Organization Registry Research Organization Registry (ROR) is a community-led database that aims to provide a persistent identifier for every research organization in the world. It complements other commonly used identifiers such as ORCID for researchers and DOI for r ...

(ROR) Publications: *

Virtual International Authority File The Virtual International Authority File (VIAF) is an international authority file. It is a joint project of several national libraries and operated by the Online Computer Library Center (OCLC). History Discussion about having a common ...

(VIAF) *

International Standard Name Identifier The International Standard Name Identifier (ISNI) is an identifier system for uniquely identifying the public identities of contributors to media content such as books, television programmes, and newspaper articles. Such an identifier consists of ...

(ISNI) *

International Standard Book Number The International Standard Book Number (ISBN) is a numeric commercial book identifier that is intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency. An ISBN is assigned to each separate edition an ...

(ISBN)

Uniform Resource Identifiers A Uniform Resource Identifier (URI) is a unique sequence of characters that identifies a logical or physical resource used by web technologies. URIs may be used to identify anything, including real-world objects, such as people and places, conc ...

: *

Archival Resource Key An Archival Resource Key (ARK) is a multi-purpose URL suited to being a persistent identifier for information objects of any type. It is widely used by libraries, data centers, archives, museums, publishers, and government agencies to provide re ...

(ARK), with 8.2 billion ARKs issued. *

Digital Object Identifier A digital object identifier (DOI) is a persistent identifier or handle used to uniquely identify various objects, standardized by the International Organization for Standardization (ISO). DOIs are an implementation of the Handle System; the ...

(DOI), with 200 million DOIs issued. *

Magnet link Magnet is a URI scheme that defines the format of magnet links, a de facto standard for identifying files ( URN) by their content, via cryptographic hash value rather than by their location. Although magnet links can be used in a number of co ...

(decentralized, with BitTorrent) *

Uniform Resource Name A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) that uses the scheme. URNs are globally unique persistent identifiers assigned within defined namespaces so they will be available for a long period of time, even after the res ...

s (URNs) *

Extensible Resource Identifier An Extensible Resource Identifier (abbreviated XRI) is a scheme and resolution protocol for abstract identifiers compatible with Uniform Resource Identifiers and Internationalized Resource Identifiers, developed by the XRI Technical Committee at O ...

s (XRIs) *

Persistent Uniform Resource Locator A persistent uniform resource locator (PURL) is a uniform resource locator (URL) (i.e., location-based uniform resource identifier or URI) that is used to redirect to the location of the requested web resource. PURLs redirect HTTP clients using ...

s (PURLs) Combined persistent identifier and archiving functionality is provided by services such as the

Internet Archive The Internet Archive is an American digital library with the stated mission of "universal access to all knowledge". It provides free public access to collections of digitized materials, including websites, software applications/games, music, ...

perma.cc Perma.cc is a web archiving service for legal and academic citations founded by the Harvard Library Innovation Lab in 2013. Concept Perma.cc was created in response to studies showing high incidences of link rot in both academic publications an ...

, archive.today, and

WebCite WebCite was an on-demand archive site, designed to digitally preserve scientific and educationally important material on the web by taking snapshots of Internet contents as they existed at the time when a blogger or a scholar cited or quoted ...

such that anyone can archive a web page to prevent link rot of a URL.

References

External links

*Juha Hakala
"Persistent identifiers – an overview."
Posted to Technology Watch Report (TWR): Standards in Metadata and Interoperability, 13 Oct 2010. *Hans-Werner Hilse and Jochen Kothe,