Information Technology Reference
In-Depth Information
Chapter 12
Basic Preservation Strategies
Strategy without tactics is the slowest route to victory. Tactics without strategy is the
noise before defeat.
(Sun Tzu)
There are a number of basic preservation strategies upon which one can build more
complex strategies. These are the ones which are described explicitly or implicitly
by OAIS, based around ensuring that the digital object will be usable and under-
standable to the Designated Community. Of course one also has to maintain the
trail of information to support evidence
of authenticity
and other PDI
.
Many publications on digital preservation say that the available strategies may
be summed up in the phrase “emulate or migrate”. We show here that this is
inadequate.
OAIS discusses some important aspects of information preservation as follows.
The fast-changing nature of the computer industry and the ephemeral nature of
electronic data storage media are at odds with the key purpose of an OAIS: to pre-
serve information over a long period of time. No matter how well an OAIS maintains
its current holdings, it will eventually need to migrate much of its holdings to dif-
ferent media (which may or may not involve changing the bit sequences) and/or
to a different hardware or software environment to keep them accessible. Today's
digital data storage media can typically be kept at most a few decades before the
probability of irreversible loss of data becomes too high to ignore. Further, the rapid
pace of technology evolution makes many systems much less cost-effective after
only a few years. In addition to the technology changes there will be changes to the
Knowledge Base of the Designated Community which will affect the Representation
Information needed.
There are a number of fundamental approaches to information preservation. In
the first the Content Data Object remains in its original form, and access and use is
achieved by providing adequate descriptions of the digital encoding with Structure
and Semantic Representation Information; in some cases the original access and
use mechanisms are adequate, in which case software emulation (using Other
Representation Information) may be useful, although this tends to limit the ways
