To make sure PIDs stay active and resolvable steps have to be taken to ensure they are maintained. The options of signing up to an initiative requiring persistence, adopting an internal policy or utilising a third party service, are described in more detail.

Local persistence

Many heritage organisations are long-lived and have a public remit to preserve their collections. As a tool to enable that activity, it may not be necessary to explicitly mention persistent identifiers as part of that remit.

The Natural History Museum's collection management system, EMu, creates GUIDs when records are saved. These are used to create links in the data portal to digitised collection items. The GUIDs are made up of an alphanumeric string. The NHM commits to maintain these links, although there is no policy or contractual commitment to do so. You can read more about this in the case study report.

Royal Botanic Garden Edinburgh was involved in the development of CETAF Stable Identifiers which require the organisation to guarantee the persistence of the links. There is no policy requirement and in the development of the identifiers the organisations involved took the view that those creating the identifiers were generally long-lasting heritage organisations and therefore could guarantee persistence. You can read more about this in a forthcoming case study report.

Policy

A persistence policy for identifiers creates a publicly visible and explicit organisational commitment to persistence and helps to raise the awareness of that commitment throughout the organisation. A policy also allows for governance and responsibilities to be set out to underwrite persistence, helping to ensure it beyond the lifetime of any one service or platform used by the organisation.

Any type of persistent identifier can be said to support persistence, with the appropriate governance that can publicly reassure users of that commitment, e.g. URIs, ARKs, PURLs.

The British Library assigns ARK identifiers to its collection content but, to make sure it and the other identifiers it uses remain accessible, and to guard against institutional memory loss that may come about due to staff changes, it is adopting a persistent identifier policy to govern its use of persistent identifiers. The purpose of the Library’s policy is to ensure continued good practice as well as increasing the assignment of identifiers across entities in the Library's collections. It also defines the Library's approach to their management and use of identifiers both new and existing.

The policy is in draft form and will be publicly available by late 2021. It is informed by the PID policy recently published by the Bibliotheque Nationale de France. More information about the British Library's use of identifiers is contained in the case study report.

PID services to guarantee persistence

PIDs such as DOIs have global governance in place that underwrites persistence. For example, in order to mint DOIs you are contractually obliged to keep them resolvable, even if only to a ‘tombstone’ page when the resource is no longer available. The community of DOI users are also able to transfer ownership, so that the persistence of DOIs can be guaranteed beyond organisational lifetimes. It depends on the type of organisation and the type of metadata you have for your collection whether or not a particular PID service will be suitable for your organisation.

Effort

The effort of maintaining the persistence of identifiers is itself not high beyond keeping webpages accessible. Most effort will be concentrated on the development of any policy and associated governance, or setting up appropriate processes to ensuring contractual compliance if using systems like DOIs. More long term, effort needs to be factored in when planning for systems or content migrations to make sure that persistent links remain resolvable.