Digital Preservation Technical Paper

Expression of PUIDs as info URIs

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Expression of PUIDs as info URIs

In order to allow PUIDs to be expressed as Uniform Resource Identifiers (URIs), and make those identifiers available for public use in Web-based description technologies, the PUID scheme has been registered as a namespace under the info URI scheme. This scheme has been developed by the library and publishing communities to facilitate the referencing by URIs of information assets which have identifiers in public namespaces but have no representation within the URI allocation. It provides a simple URI registration mechanism to support the referencing of public information assets in advance of any possible subsequent URI scheme or URN namespace application.

The PUID scheme is registered with the info URI registry using the namespace ‘pronom’. A PUID identifier can be expressed as an info URI as follows:

The example PUID given in Section 3 would therefore be expressed as follows:

Full details of the “info:pronom” namespace are available from the info URI registry, at

Use of PUIDs
It is anticipated that PUIDs will primarily be used within managed electronic information environments, such as Electronic Records Management Systems (ERMS) and digital repositories. As such, PUIDs will normally be automatically assigned to individual electronic objects in one of two ways:

  • At the point of creation, either by the authoring software or the ERMS.

  • At any subsequent point in the object’s life cycle, either as part of the ingest process for an ERMS or digital repository, or through the use of separate file format identification tools.

An example of a file format identification tool which supports PUIDs is TNA’s DROID (Digital Record Object Identification) software. This freely-available tool performs automatic identification of the formats of digital objects, and will report the corresponding PUID (where assigned) for all identified objects. DROID provides a command line API to support integration with ERMS or repository software, and the identification results can be returned as an XML file, to allow simple transformation into any metadata scheme.

Neither the PUID scheme, nor its expression as an info URI, support any inherent dereferencing mechanism, i.e. a PUID does not resolve to a URL. However, TNA is planning to develop a range of services to expose PRONOM registry content, including a resolution service for PUIDs.
  1. Scheme Administration

The PRONOM service and namespace, and the PUID scheme, are administered by the Digital Preservation Department of The National Archives. PUIDs are only authorised and assigned by TNA, and disseminated via the PRONOM registry (

The coverage of the PUID scheme is intended to be as extensive as possible, but with a current emphasis on file formats which may be used to create and store electronic records. New PUIDs are assigned on a regular basis, both to reflect new developments and to extend coverage of existing formats. In order to support the persistence and consistency of the scheme, new PUIDs are only assigned after thorough research and evaluation, to ensure that all variants of a given format are sufficiently understood to assign new PUIDs with confidence.
Requests for new PUIDs are particularly encouraged from those responsible for the management of ERMS, other digital preservation facilities, and from software and format specification developers. Submissions of supporting technical information on file formats and software tools for inclusion on PRONOM are also welcomed. TNA also welcomes external requests for the assignment of new PUIDs. Requests should be submitted by email to Upon receipt, TNA will evaluate the request, undertake any necessary research, and assign a PUID as appropriate. The submitter will be notified of the result of the request by email, within 10 working days, although the time required to research and assign a new PUID, and to publish it via the registry, will be dependent upon the availability of the necessary technical information, and the complexity of the format.

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