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 needs to establish a unique, persistent identifier (PID) for every entity referred to by its digital information.
Beyond just supplying another ID, PID systems 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.
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 things one might want to discuss or refer to already have IDs within existing local databases or catalogue systems. The purpose of a PID system 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.
NG Persistent identifiers take the form of Linked (Open) Data dereferenceable URIs. The National Gallery mints its own PIDs for its own resources, using the namespace http://data.ng-london.org.uk/resource/. Additional internal systems are being built to allocate PIDs and, where relevant, write them into systems which store digital data (e.g. TMS, EOS, CALM, CID, Extensis).Other PIDs (e.g. ISBNs, DOIs, LOD URIs from other data sources) will also be recorded, where they exist, to ensure that NG data is interoperable.
PIDs will also be used within the NG IIIF server to present public images. This system will use a different namespace and a variable structure based on application.