2.2.1 INFORMATION DEFINITION
A clear definition of information is central to the ability of an OAIS to preserve it. While formal modeling of information is provided in section 4, some key concepts are provided in this subsection.
A person, or system, can be said to have a Knowledge Base, which allows that person or system to understand received information. For example, a person who has a Knowledge Base that includes an understanding of English will be able to read, and understand, an English text.
Information is defined as any type of knowledge that can be exchanged, and this information is always expressed (i.e., represented) by some type of data in an exchange. For example, the information in a hardcopy book is typically expressed by the observable characters (the data) which, when they are combined with a knowledge of the language used (the Knowledge Base), are converted to more meaningful information. If the recipient does not already include English in its Knowledge Base, then the English text (the data) needs to be accompanied by English dictionary and grammar information (i.e., Representation Information) in a form that is understandable using the recipient’s Knowledge Base. The Designated Community, and its associated Knowledge Base, for whom the information is being preserved by the Archive is defined by that Archive, and that Knowledge Base will, as described below, change over time. The definition of Designated Community may be subject to agreement with funders and other stakeholders.
Similarly, the information stored within a CD-ROM file is expressed by the bits (the data) it contains which, when they are combined with the Representation Information for those bits,are converted to more meaningful information as long as the Representation Information is understandable using the recipient’s Knowledge Base. For example, assume the bits represent an ASCII table of numbers giving the coordinates of a location on the Earth measured in degrees latitude and longitude. The Representation Information will typically include the definition of ASCII together with descriptions of the format of the numbers and their locations in the file, their definitions as latitude and longitude, and the definition of their units as degrees. It may also include additional meaning that is assigned to the table. Another example of Representation Information for a bit sequence which is a FITS file might consist of the FITS standard which defines the format plus a dictionary which defines the meaning of keywords in the file which are not part of the standard. In general, it can be said that ‘Data interpreted using its Representation Information yields Information’, and this is shown schematically in figure 2-2.
Figure 2-2: Obtaining Information from Data
In order for this Information Object to be successfully preserved, it is critical for an OAIS to identify clearly and to understand clearly the Data Object and its associated Representation Information. For digital information, this means the OAIS must clearly identify the bits and the Representation Information that applies to those bits. This required transparency to the bit level is a distinguishing feature of digital information preservation, and it runs counter to object-oriented concepts which try to hide these implementation issues. This presents a significant challenge to the preservation of digital information.
As a further complication, the recursive nature of Representation Information, which typically is composed of its own data and its own Representation Information, typically leads to a network of Representation Information objects. Since a key purpose of an OAIS is to preserve information for a Designated Community, the OAIS must understand the Knowledge Base of its Designated Community to understand the minimum Representation Information that must be maintained. The OAIS should then make a decision between maintaining the minimum Representation Information needed for its Designated Community, or maintaining a larger amount of Representation Information that may allow understanding by a larger Consumer community with a less specialized Knowledge Base, which would be the equivalent of extending the definition of the Designated Community. Over time, evolution of the Designated Community’s Knowledge Base may require updates to the Representation Information to ensure continued understanding.
The choice, for an OAIS, to collect all the relevant Representation Information or to reference its existence in another trusted or partner OAIS Archive, is an implementation and organization decision.
As a practical matter, software, some of which may itself be Representation Information, is used to access the Information Object, and it will incorporate some understanding of the network of Representation Information objects involved. However, this software should not be used as rationale for avoiding identifying and gathering readily understandable Representation Information that defines the Information Object, because it is harder to preserve working software than to preserve information in digital or hardcopy forms.
The OAIS reference model emphasizes the preservation of information content. As digital technology develops, multimedia technology and the dependency on complex interplay between the data and presentation technologies will lead some organizations to require that the look and feel of the original presentation of the information be preserved. This type of preservation requirement may necessitate that the software programs and interfaces used to access the data be preserved. This problem may be further complicated by the proprietary nature of some of the software. Various techniques for preserving the look and feel of information access are currently the subject of research and prototyping. These techniques, which include hardware level emulation, emulation of various common service APIs, and the development of virtual machines, investigate the preservation of the original bit stream and software across technology. Though the OAIS reference model does not focus on these emerging techniques, it should provide an architectural basis for the prototyping and comparison of these techniques. A more detailed discussion of the issues involved in the preservation of look and feel of information access can be found in 5.2 of this document.
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