2.2.2 INFORMATION PACKAGE DEFINITION
The definition of an Information Object is applicable to all the information types discussed in this and the following subsections. In other words, they all have associated Representation Information, although this is usually not shown explicitly.
Every submission of information to an OAIS by a Producer, and every dissemination of information to a Consumer, occurs as one or more discrete transmissions. Therefore, it is convenient to define the concept of an Information Package.
An Information Package is a conceptual container of two types of information called Content Information and Preservation Description Information (PDI). The Content Information and PDI are viewed as being encapsulated and identifiable by the Packaging Information. The resulting package is viewed as being discoverable by virtue of the Descriptive Information.
These Information Package relationships are shown schematically in figure 2-3.
Figure 2-3: Information Package Concepts and Relationships
The Content Information is that information which is the original target of preservation. It consists of the Content Data Object (Physical Object or Digital Object, i.e., bits) and its associated Representation Information needed to make the Content Data Object understandable to the Designated Community. For example, the Content Data Object may be an image that is provided as the bit content of one CD-ROM file together with other files, on the same CD-ROM, that contain Representation Information.
Only after the Content Information has been clearly defined can an assessment of the Preservation Description Information be made. The Preservation Description Information applies to the Content Information and is needed to preserve the Content Information, to ensure it is clearly identified, and to understand the environment in which the Content Information was created. The Preservation Description Information is divided into five types of preserving information called Provenance, Context, Reference, Fixity and Access Rights. Briefly, they are the following:
– Provenance describes the source of the Content Information, who has had custody of it since its origination, and its history (including processing history).
– Context describes how the Content Information relates to other information outside the Information Package. For example, it would describe why the Content Information was produced, and it may include a description of how it relates to another Content Information object that is available.
– Reference provides one or more identifiers, or systems of identifiers, by which the Content Information may be uniquely identified. Examples include an ISBN for a book, or a set of attributes that distinguish one instance of Content Information from another.
– Fixity provides a wrapper, or protective shield, that protects the Content Information from undocumented alteration. For example, it may involve a checksum over the Content Information of a digital Information Package.
– Access Rights provide the terms of access, including preservation, distribution, and usage of Content Information. For example, it would contain the statements to grant the OAIS permissions for preservation operations, licensing offers (for distribution), specifications for rights enforcement measures, as well as access control specifications.
The Packaging Information is that information which, either actually or logically, binds, identifies and relates the Content Information and PDI. For example, if the Content Information and PDI are identified as being the content of specific files on a CD-ROM, then the Packaging Information would include the ISO 9660 volume/file structure on the CD- ROM, as well as the names and directory information of the files on CD-ROM disk. Other examples of packaging include XFDU (reference [D11]) where the Packaging Information would be the file identifier and the definition of the packaging method.
The Descriptive Information is that information which is used to discover which package has the Content Information of interest. Depending on the setting, this may be no more than a descriptive title of the Information Package that appears in some message, or it may be a full set of attributes that are searchable in a catalog service.
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