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Persistent Identifiers at Washington University

University Libraries Services for DOIs, ARKs, and other information about persistent identifiers

What is a Persistent Identifier (PID)?

Washington University in St. Louis can only provide DOIs and ARKs for faculty, staff, students, and researchers affiliated with the university.

A persistent identifier (PI or PID) is a long-lasting reference to a document, file, web page, or other digital object. Most PIDs have a unique identifier which is linked to the current address of the metadata or content. Unlike URLs, PIDs are often provided by services that allow you to update the location of the object so that the identifier consistently points to the right place without breaking.

The long-term persistence of identifiers for objects, contributors, and organizations is vital to robust data management strategies. Publishers, funders, and other organizations have implemented PIDs in their established research workflows to enable the creation of trusted digital connections between objects, contributors, and organizations.

PID is a new name for a concept that has been a part of publishing for decades. In the past publishers used identifiers such as ISBNs and ISSNs to distinguish unique textual objects. However, the proliferation of digitally available research and technical publications has created a need for machine-readable, interoperable PIDs. Machine-readable PIDs such as DOIs and ORCID iDs are valuable assets in enabling information sharing across systems.

Persistent Identifiers covered in this guide:

  • Digital Object Identifier (DOI)
  • Archival Resource Key (ARK

Note that DOIs are permanent and cannot be deleted.  ARKs can be used to track a resource in development before a decision is made as to whether or not the resource will be made permanent, at which point a DOI can be assigned. 

Archival Resources Key (ARK)

An ARK identifier is a “specially constructed, globally unique, actionable URL and the ARK scheme is underpinned by three requirements based on links: from the object to a promise for stewardship, from the object to metadata which describes it, and to the object itself”.

Digital Object Identifier (DOI)

A DOI is a “digital identifier of an object,” not an identifier of a digital object—that is, DOIs can be assigned to any object, whether physical or digital. DOIs serve as “unique, permanent numbers assigned to specific objects, which remain unchanged”. DOIs are the most common type of identifier for digital objects, particularly for scholarly, research, and technical publications.

Handle (HNDL)

The Handle or HNDL system is a “distributed information system designed to provide an efficient, extensible, and secured global name service for use on networks such as the Internet” [3]. Handle serves primarily as an underlying architecture for identifier systems such as the DOI system, but it can also be used as an identifier system on its own.

Persistent Uniform Resource Locator (PURL)

The PURL system provides “a naming and resolution service for general internet resources” [6]. A PURL is a URL that “points to a resolution service instead of the actual location of a digital resource,” and the resolution service then redirects to the current URL of the resource. ARKs, DOIs, and HNDLs are all forms of PURLs, long-lasting URLs that point to resolution services that maintain information about the current location of a resource.

Open Researcher and Contributor ID (ORCID)

ORCIDs enable identification, linking and discovery between researchers. ORCID provides a registry where individuals may obtain a unique PID, which can be used in connection with their research and scholarly workflows. For more information about ORCIDs, visit the Libguide ORCiD for Researchers and Students


Special thanks to Jesse Long (, Jennifer Muilenburg (, and Anna Neatrour ( for permission to use text from their Libguides on persistent identifiers.