Following the release of version 4 of the PRONOM technical registry and the DROID automatic file format identification tool in October 2005, The National Archives is pleased to announce the publication of the PRONOM Persistent Unique Identifier (PUID) Scheme.
The PRONOM Unique Identifier (PUID) is an extensible scheme for providing persistent, unique and unambiguous identifiers for file formats held in the PRONOM technical registry. Such identifiers are fundamental to the exchange and management of digital objects, by allowing human or automated user agents to unambiguously identify, and share that identification of, the representation information required to support access to an object. This is a virtue both of the inherent uniqueness of the identifier, and of its binding to a definitive description of the representation information in a registry such as PRONOM.
At present, the PUID scheme has been confined to one particular class of representation information: the format in which a digital object is encoded. Formats are considered a particular priority for such a scheme. No existing, universally applicable system provides for this. Unix 'magic numbers' and Macintosh data-forks do provide some of this functionality, but the same is not true within DOS or Microsoft Windows environments. The three-character file extension is neither standardised nor unique, and is interpreted differently by different environments. Equally, the IANA MIME-type scheme does not provide sufficient granularity or coverage to satisfy the requirements for unique identifiers. The PUID scheme has been developed for the single purpose of providing such identifiers. In the first instance, PUIDs have been assigned to over 130 of the most common formats, and more being added on a regular basis. The DROID tool is now also capable of assigning these identifiers to files, through its live update facility with the PRONOM database.
The scheme has been adopted as the recommended encoding scheme for describing file formats in the latest version of e-Government Metadata Standard http://www.govtalk.gov.uk/schemasstandards/metadata_document.asp?docnum=872. This means that, for the first time, a consistent, persistent and highly granular scheme for describing file formats will be in use across the UK government. The scheme is designed to be extensible, and will be expanded in future to include other classes of representation information in PRONOM, such as compression methods, character encoding schemes, and operating systems.
PUIDs can be expressed as Uniform Resource Identifiers (URIs) using the "info:pronom/" namespace, details of which are available from the info URI registry http://info-uri.info/registry/OAIHandler?verb=GetRecord&metadataPrefix=reg&identifier=info:pronom/. Neither the PUID scheme, nor its expression as an info URI, supports any inherent dereferencing mechanism, i.e. a PUID does not resolve to a Uniform Resource Locator (URL). However, The National Archives is planning to develop a range of services to expose PRONOM registry content, including a resolution service for PUIDs. Further information and technical documentation on the PUID scheme is available at http://www.nationalarchives.gov.uk/aboutapps/pronom/puid.htm.
The assignment of new PUIDs is managed by The National Archives, and suggestions for new PUIDs are welcomed. For further information, feedback, or comments, please email [log in to unmask]
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