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Persistent Identifiers (PIDs)

What are Persistent Identifiers, and how does the Gallery use them?

In order to interlink Gallery digital information which is currently held in multiple systems, and to share its data unambiguously with external users (e.g. research projects), the National Gallery has established a unique, dereferenceable persistent identifier (PID) for every entity referred to by its digital information.

National Gallery PID format

National Gallery PIDs take the form of Linked (Open) Data dereferenceable URIs, in the format: 

namespace/AAAA-AAAA-AAAA-AAAA

where:

  • The namespace is: https://data.ng.ac.uk
  • A is any alphanumeric character (uppercase letter and numbers), and together they represent a unique NG PID.

E.g.

https://data.ng.ac.uk/0F6J-0001-0000-0000

is the PID for NG35, Titian's Bacchus and Ariadne

Initially we will be using 16 characters, which will allow for 3616 possible PIDs; but the system has been built to allow additional sets of 4 characters to be added to scale the number further if required.

National Gallery PID policy

We mint our own PIDs for entities recorded in Gallery systems. In the case of our objects, and other data which we create (e.g. images), these should be taken as canonical. For other entities (people, organisations, places, concepts, publications, etc.) we will record and publish external identifiers (e.g. ISBNs, DOIs, Linked Data URIs from other data sources) where possible, to ensure that our data is interoperable.

What are PIDs?

A persistent identifier (PI or PID) is a long-lasting generic reference to an image, document, file, web page, or digital description of any physical thing or concept that one might want to describe or discuss.

Many such entities already have IDs within existing local databases or catalogue systems. The purpose of a PID is to provide unique generic identifiers that can be used and re-used across multiple systems, particularly in relation to publishing information that can be accessed over the Internet.

Beyond just supplying another ID, PIDs are typically designed to be actionable, and are generally presented in the form of web based URLs that provide further details about the thing being referenced and links to more information or additional systems.