oais1.jpgNoted from the OAIS model.

SIPs get transformed into one of these for preservation. The AIP “is defined to provide a concise way of referring to a set of information that has, in principle, all the qualities needed for permanent, or indefinite, Long Term Preservation of a designated Information Object …. though the implementation of the AIP may vary from archive to archive, the specification of the AIP as a container that contains all the needed information to allow Long Term Preservation and access to archive holdings remains valid” (4.2.2.2 and 3).

The AIP has a complete set of PDI for the associated Content information. The Packaging Information of the AIP will conform to OAIS internal data formatting and documentation standards, and may vary over time as the OAIS changes its practices. Transforming a SIP into an AIP “may involve file format conversions, data representation conversions or reorganisation of the content information” (4.1.1.2).

AIPs are managed within the OAIS by the Archival storage entity (4.1). Functions include managing the storage, refreshing the media, performing routine and special error checking, and providing disaster recovery capabilities: see 4.1.1.3 for details of all these.

Some AIPs may only exist as the output of algorithms operating on other AIPs (3.2.6).

Subtypes

Section 4.2.2.4 of the model refers to two AIP subtypes. The Archival Information Unit is the “atom” which the archive is asked to store. A single AIU contains exactly one Content Information object (which in turn may be multiple files, however) and exactly one set of PDI (4.2.2.5). The example they give is a digital movie. This AIU would contain three objects:

  • the digital encoding of the movie in a proprietary format
  • the Representation Information needed to understand this format (these two form the Content Info)
  • PDI: date of creation, featured actors, movie studio, etc, and a checksum for integrity.

The second subtype is the Archival Information Collection. There might be millions of AIUs, you see, so the answer is to aggregate them into AICs using criteria determined by the archivist (4.2.2.7). A single AIP can belong to multiple AICs. The AIC itself is a complete AIP which contains PDI. The PDI provides further info such as when and why it was created, context to related AICs, desired levels of security etc.

Borghoff et al point out that OAIS does not allow for changes in stored AIPs. Instead, the AIP must be extracted from the archive as a DIP, modified, and then resubmitted as a SIP. “We hope that for trivial changes the archiving systems will provide more pragmatic and simpler solutions” (p. 52).

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