Explain! Identifier

A persistent identifier (short: PID) is a unique string assigned to a digital resource. They facilitate finding these digital research resources and prevent frustration and loss of information caused by broken links. PIDs refer to a resource independently of its physical storage location and enables persistent access. In addition, PIDs provide the possibility to be enriched with metadata describing the identified resource.

With a PID your data becomes referable and citable in scientific publications.

In the scientific world several PID systems exist, but they have some aspects in common:

1. All metadata belonging to the object have to be registered only once.
2. Changes of the location of the registered object have to be supplemented with the respective resolving agency.
3. While the URL of a resource can change if it is moved to different location, the PID remains the same and ensures the unique long term identification of the resource.

PIDs make it easy to link and cite digital resources in a scientific way.

Common PID systems for science

At the moment the following PID systems are most commonly used in the scientific context:

Handles (hdl)

The handle system is a technology specification which can be used to assign, to manage, and to resolve PIDs. Handles consist of a prefix which identifies a “naming authority” and a suffix which gives the “local name” of a resource. The prefixes are issued to naming authorities – similar to domain names. If you have a handle like hdl:4263537/4086, the prefix 4263537 belongs to the organisation which creates the handle, and the suffix 4086to the resource itself. The naming authority may create any number of handles, with unique “local names”, within their prefixes. To find a resource referenced by a handle you have two options: Either enter the handle into the search bar on hdl.handle.net or use it directly as a URL http://hdl.handle.net/4263537/4086.
More information about handles can be found here: http://www.handle.net

Digital Object Identifiers (DOI)

The DOI system is an identifier scheme administered by the International DOI Foundation. It is built on the Handle System but has its own conventions and an independent business model. A DOI looks like this doi:10.1000/182. Like in the handle system the DOI prefix and suffix represent the organisation and the resource respectively. What is unique about DOIs is their starting number 10.. You can resolve a DOI at www.doi.org or use DOIs as URL information like https://doi.org/1000/182.
More information about DOIs can be found at DOI.org or on the website of the DCC.

Persistent URLs (PURLs)

A PURL is a form of Uniform Resource Locator (URL) that is used to redirect to the location of the requested web resource. PURLs are used to curate the URL resolution process. The PURL concept was developed by OCLC (Online Computer Library Center) in 1995.

Archival Resource Key Identifiers (ARKs)

An Archival Resource Key is another kind of Uniform Resource Locator (URL). ARKs can be used for information objects of any kind. They can be maintained and resolved locally via software, services or central resolver.

ORCID

PIDs can also be used to uniquely identify researchers. This can be quite useful if you have a prevalent name or change your name during your research career. ORCID for example is a PID-system for researchers.

How to get a PID?

To assign a PID to a digital resource, it is necessary to approach a PID registration agency that controls the distribution and ensures the resolution of PIDs. Please look at our How-to: Getting an identifier to learn how this works at the Göttingen Campus.

Further information

Examples of Persistent Identifiers
ANDS pages on citation and identifiers
DARIAH-DE information about PIDs