Workbook on Digital Private Papers > Introduction > Introduction to OAIS

Introduction to OAIS

Overview of the OAIS model: Information model (OAIS 2.2)

In addition to defining the parties involved in the long-term preservation of digital materials, OAIS provides an information model for managing the digital materials as they pass through the system. A significant component of this model is the Information Package (IP). Each IP consists of:

OAIS outlines three types of Information Package:

SIP

At the SIP stage, the metadata accompanying the digital object is, ideally, supplied by the Producer who is generally the original creator of the material; in the case of personal archives it is perhaps more likely that a digital archivist working with the creator will provide the metadata. At this stage, the metadata will probably lack structure and may not be comprehensive at all levels of the archive. SIPs may also be supplied to an OAIS from another digital repository. Where another digital repository has supplied SIPs, the use of interoperable metadata standards will minimise the effort required to ingest the material into the new repository.

AIP

At the AIP stage, the SIPs are prepared for preservation. During this process, the digital materials submitted for preservation are known as Content Data Objects and they are combined with the Preservation Description Information (PDI, see OAIS 4.2.1.4.2) needed to administer their preservation. OAIS breaks the PDI down into four sections:

Preservation Description Information

OAIS also requires the archive to maintain the Representation Information required to render the object intelligible to its designated community. This might include information regarding the hardware and software environment needed to view the content data object.

Detailed information on the AIP can be found in OAIS 4.2.2.3.

DIP

The DIP stage happens when a user (or Consumer in OAIS terms!) requests a digital object or group of objects from the OAIS. The OAIS supplies the object(s) packaged as a DIP comprising the object and relevant metadata. It is likely that the metadata accompanying the object at this stage will be more descriptive than technical; the end user is unlikely to want to see complicated metadata relating to fixity or representation. In all instances, the Knowledge Base of the OAIS' Designated Community will guide the type and extent of metadata supplied.

METS and Information Packages

The METS (Metadata Encoding and Transmission Standard) standard was designed to fulfil the OAIS 'Information Package' concept. METS can be implemented in many ways, but the key consideration for preservation repositories is that METS provides a means of associating all the metadata pertaining to an object, including that object's relationships with other objects, with the object.

Representation Information

Representation Information is an important part of the OAIS information model. Representation Information is used to interpret a Data Object so that it can be rendered into a useful Information Object. Representation Information permits the expression of dependencies within a digital archive. Since many repositories contain broadly similar objects, central Representation Information registries that can be used by several repositories are being developed; one example is the Digital Curation Centre's Representation Information Registry (under development). See OAIS 2.2.1 and 4.2.1.3 for further information.

Descriptive Information

OAIS also includes descriptive metadata as part of its information model. Descriptive metadata is not part of the Information Package, rather it describes the package.