Workbook on Digital Private Papers > Administrative and preservation metadata > Preservation metadata
Preservation metadata
Preservation metadata and OAIS
Much of the work on developing preservation metadata for digital repositories is informed by the Reference Model for an Open Archival Information System (OAIS); it is therefore worth examining what information OAIS deems necessary for the long-term preservation of digital materials. OAIS specifies that all Content Data Objects which a repository intends to preserve should have relevant Representation Information, Preservation Description Information, Packaging and Descriptive Information.
Representation Information (RI) provides structural and semantic information that permits the interpretation of Content Data Objects (i.e. the archival material accessioned) so that they may be rendered accessible: translating bits into information that is meaningful to the repository’s Designated Community (usually a variety of researchers in the case of archival institutions).
Classes of RI relevant to many individual objects can be identified; RI for common digital object types could therefore be held in one or more central registries, or in a local registry. RI itself may also be in digital form and require its own RI in order to be fully understood; the repository must therefore determine the level of RI to be held locally and/or referred to in external registries.
Example:
A repository accessions a spreadsheet of names and addresses in Lotus 4 spreadsheet format. The spreadsheet is a series of meaningless bits without the RI required to render it visible to the human eye. An understanding of this RI is built into the application software that was originally used to read and write the spreadsheet (Lotus 1-2-3, version 4) and now needs to be made accessible to the archiving repository. The repository may therefore wish to record or refer to information about the Lotus 4 spreadsheet format. If the format documentation is published in Portable Document Format 1.4, then the repository may also require RI to interpret and render files conforming to the PDF 1.4 format.
Preservation Description Information provides information about the individual content data to be preserved. OAIS adopts the classification identified in the 1996 report by Donald Waters and John Garrett entitled Preserving Digital Information, which splits this information into four groups:
- Reference information - allows for consistent, enduring and unique identification.
- Provenance information - details the origin and custody of an information object, including events in its life once submitted to the repository.
- Context information - documents the relationship of an information object with its environment, including why it was created and relationships with other information objects.
- Fixity information - documents authenticity using mechanisms which evidence that no undocumented alterations have been applied.
Packaging Information binds content information and its metadata together in an Information Package so that the relationship between the two can be sustained over time. METS is one example of a metadata standard designed to package several bits of metadata and the content information to which the metadata refers.
Descriptive Information does not form part of the Information Package; rather it functions to describe the Package, enhancing access to the content information via finding aids and search and discovery tools. At the preservation stage (represented in OAIS by the Archival Information Package), descriptive information about personal digital archives is likely to be minimal, consisting of automatically extracted information at the inventory level and collection or accession-level contextual information. The depth and quality of descriptive information can be improved when the archive is formally arranged and described (see Chapter 06 Arranging and cataloguing digital and hybrid archives) for researcher access, in the form of Dissemination Information Packages and an EAD catalogue. However, some degree of descriptive metadata is essential for long-term preservation, not least because a long period is likely to elapse before archived digital objects are subject to detailed cataloging.
