What are PIDs?
A Persistent Identifier (PID) is a unique string registered to an object. It provides a single consistent way to point to or reference the object even as the object’s location, underlying infrastructure, or web address changes with time. Typically, a PID does not only provide the location of the data the PID is referring to but also additional metadata (e.g. identifier type, owner, etc.).
The PID string itself consists of a prefix and a suffix separated by a forward slash (/). The prefix is a single number and groups together one or more suffixes maintained by an institution or individual. The suffix is a unique alphanumeric string of characters. The combination of the pre- and suffix uniquely identifies a specific object at a specific location.
Example of a PID from the SURF repository:
11112/SURF.82df4163-f7c855ca
Prefix: 11112
Suffix: SURF.82df4163-f7c855ca
To retrieve the object or any metadata about it, a resolver is required.
Why PIDs?
PIDs ensure that all elements of your research are uniquely identifiable and accessible: by humans as well as machines. Research data has grown exponentially over the last couple decades and may be housed across various data centres and recorded within various types of media, making it difficult to consolidate. The storage locations and infrastructures of the data themselves are also subject to change, which can make published references to data obsolete. This makes it increasingly difficult and laborious to guarantee the findability and accessibility of your data. At the same time, guaranteeing findability and accessibility is important to facilitate reproducibility and reuse. PIDs offer a simple way to consolidate and trace your data no matter what changes time may bring.
Resolving PIDs
The string of the PID itself has no inherent meaning or information attached to it beyond it’s uniqueness. Rather it is used by the resolver to retrieve the object, it’s location and/or it’s metadata. PIDs registered with SURF, through the ePIC PID consortium, use the Handle service to resolve. You can read more about the Handle service below.
As an example, the PID 11304/2e873bd8-b988-11e3-8cd7-14feb57d12b9 can be resolved using the Handle service proxy URL followed by the PID itself:
http://hdl.handle.net/11304/2e873bd8-b988-11e3-8cd7-14feb57d12b9
Which currently redirects to the webpage: https://b2share.eudat.eu/records/e764dd9162c84a7e929887d3989fe4d1
(And formerly redirected to the webpage: https://b2share.eudat.eu/record/14)
This webpage functions as a landing page and contains corresponding metadata as well as links to the raw dataset files.
ePIC consortium
SURF offers a highly reliable, redundant and performant PID provisioning service in cooperation with the Persistent Identifiers for eResearch (ePIC) consortium, formerly known as the European Persistent Identifier Consortium (EPIC).ePIC provides new prefixes in the namespace “21.” through the GWDG’s membership in DONA. ePIC provides a redundant and load-balanced setup between the international consortium’s datacenters and guarantees all time and global PID resolution availability.
Handle PIDs
The Handle System is run by the DONA foundation (Digital Object Network Architecture) on behalf of the Corporation for National Research Initiatives (CNRI) and provides a comprehensive and flexible system for assigning, managing, and resolving PIDs for digital objects and other resources on the Internet. The Handle System includes an open set of protocols, an identifier space, and an implementation of the protocols.
More info
ePIC consortium website: http://www.pidconsortium.net
Persistent Identifier Guide by the Nationaal Archief: https://www.pidwijzer.nl/en/
A Persistent Identifier (PID) policy for the European Open Science Cloud (EOSC): https://data.europa.eu/doi/10.2777/926037
PID architecture for the EOSC: https://data.europa.eu/doi/10.2777/525581
Knowledge Exchange’s report on risks and trust in pursuit of a well functioning PID infrastructure for research: https://www.knowledge-exchange.info/event/pids-risk-and-trust
Research Data Alliance’s (RDA) PID interest group: https://www.rd-alliance.org/groups/pid-interest-group.html