Preservation Description Information

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In addition to Content Information, the Archival Information Package must include information that will support the trust in, the access to and context of the Content Information over an indefinite period of time. The specific set of Information Objects, which are required for this function, is collectively called Preservation Description Information (PDI). The PDI must include information that is necessary to adequately preserve the particular Content Information with which it is associated. It is specifically focused on describing the past and present states of the Content Information, ensuring it is uniquely identifiable, and ensuring it has not been unknowingly altered.

This information is typical for all types of Archives and has been classified in the context of traditional Archives. However, the class definitions must be extended for digital Archives.

The following definitions are largely based on the categories discussed in the paper ‘Preserving Digital Information’ (reference [D2]). The relationship between the concepts in OAIS Reference Model and the Preserving Digital Information paper are discussed in annex B of this document. Table 4-1 provides illustrative examples of this information for various popular Content Information types.

Reference Information identifies, and if necessary describes, one or more mechanisms used to provide assigned identifiers for the Content Information. It also provides those identifiers that allow outside systems to refer, unambiguously, to this particular Content Information. Examples of these systems include taxonomic systems, reference systems and registration systems. In the OAIS Reference Model most if not all of this information is replicated in Package Descriptions, which enable Consumers to access Content Information of interest.

Context Information documents the relationships of the Content Information to its environment. This includes why the Content Information was created and how it relates to other Content Information objects existing elsewhere.

Provenance Information documents the history of the Content Information. This tells the origin or source of the Content Information, any changes that may have taken place since it was originated, and who has had custody of it since it was originated, providing an audit trail for the Content Information. This gives future users some assurance as to the likely reliability of the Content Information as it contributes to evidence supporting Authenticity. Provenance can be viewed as a special type of context information.

Fixity Information provides the Data integrity checks or validation/verification keys used to ensure that the particular Content Information object has not been altered in an undocumented manner. Fixity Information includes special encoding and error detection schemes that are specific to instances of Content Objects. Fixity Information does not include the integrity preserving mechanisms provided by the OAIS underlying services, error protection supplied by the media and device drivers used by Archival Storage. The Fixity Information may specify minimum quality of service requirements for these mechanisms.

Access Rights Information identifies the access restrictions pertaining to the Content Information, including the legal framework, licensing terms, and access control. It contains the access and distribution conditions stated within the Submission Agreement, related to both preservation (by the OAIS) and final usage (by the Consumer). It also includes the specifications for the application of rights enforcement measures.

These classifications provide a minimum set of PDI; they do not specify a data structure.

Table 4-1: Examples of PDI

The OAIS needs to explicitly decide what the exact definition of Content Information is in order to be able to ensure that it also has the PDI needed to preserve the Content Information. Once the Content Information has been determined, it is possible to assess the Preservation Description Information. Packaging Information

The Packaging Information is that information which, either actually or logically, binds or relates the components of the package into an identifiable entity on specific media. For example, if the Content Information and PDI are identified as being the content of specific files in a TAR file, then the Packaging Information may include the name of the TAR file and the fact that it is a TAR file including details of any specific encoding. On the other hand if the Content Information and PDI are files on a CD-ROM, then the Packaging Information may include the ISO 9660 volume/file structure on the CD-ROM. These choices are the subject of local Archive definitions or conventions. The Packaging Information does not necessarily need to be preserved by an OAIS since it does not contribute to the Content Information or the PDI. However, there are cases where the OAIS may be required to reproduce the original submission exactly. In this case the Content Information is defined to include all the bits submitted.

The OAIS should also avoid holding PDI or Content Information only in the naming conventions of directory or file name structures. These structures are most likely to be used as Packaging Information. Packaging Information is not preserved by all Digital Migrations. Any information saved in file names or directory structures may be lost when the Packaging Information is altered. The subject of Packaging Information is an important consideration to the Migration of Information within an OAIS to newer media. This subject is addressed in detail in section 5 of this document.