Information Technology Reference
In-Depth Information
description of how to interpret the string of bits as numbers representing temperature
observations measured in degrees Celsius.
Note that Knowledge is not defined in OAIS.
The accompanying definition of data is equally broad:
Data:
A reinterpretable representation of information in a formalized man-
ner suitable for communication, interpretation, or processing.
Examples of data
include a sequence of bits, a table of numbers, the characters on a page, the recording
of sounds made by a person speaking, or a moon rock specimen.
And in the case of things digital:
Digital Object:
An object composed of a set of bit sequences
.
Note that this does not mean we are restricted to a single file. The
definition includes multiple, perhaps distributed, files, or indeed a set
of network messages.
The restriction to “bits” i.e. consisting of “1” and “0”, means that
if we move to trinary (i.e. “0”, “1” and “2”) instead of binary then
we would have to change this definition, but it would not affect the
concept - however it would change the tools we could use.
One might wonder why data includes physical objects such as a “moon rock
specimen”. The answer should become clear later but in essence the answer is that
to provide a logically complete solution to digital preservation one needs, eventually,
to jump outside the digital, if only, for example, to read the label on the disk.
As to the question of length of time we need to be concerned about, OAIS pro-
vides the following pair of definitions (the text in bold italics below is taken from
OAIS):
Long Term:
A period of time long enough for there to be concern about the
impacts of changing technologies, including support for new media and data for-
mats, and of a changing Designated Community, on the information being held
in an OAIS. This period extends into the indefinite future.
Long Term Preservation:
The act of maintaining information, Independently
Understandable by a Designated Community, and with evidence supporting its
Authenticity, over the Long Term.
In other words we are not only talking about decades into the future but, as is a
common experience, we need to be concerned with the rapid change of hardware
and software, the cycle time of which may be just a few years. Of course even if an
archive is not itself looking after the digital objects over the long term, even by that
definition, the intention may be for another archive to take over later. In this case the
first archive needs to capture all the “metadata” needed so that it can hand these on
also.
