Information Technology Reference
In-Depth Information
tested to attempt an emulation of that application. However, if the consumer inter-
face is primarily one of display or other devices which affect human senses (e.g.,
sound), this reverse engineering becomes nearly impossible, because it may not be
obvious when the application runs but does not function correctly for all possi-
ble inputs. To guarantee the discovery of all such situations, it would be necessary
to record the Access Software's correctly functioning output, and preserve this
alongside the emulation. The behaviour would need to be checked with the results
obtained after from the emulation. This may be quite difficult if the application has
many different modes of operation. Further, if the application's output is primarily
sent to a display device, recording this stream does not guarantee that the display
looks the same in the new environment and therefore the combination of applica-
tion and environment may no longer be giving completely correct information to the
Consumer.
Maintaining a consistent look and feel may require, as a starting point, captur-
ing that look and feel with a separate recording to use as validation information.
In general, it may be difficult if not impossible to formally describe the look and
feel. However, a number of Transformational Information Properties may essen-
tially define criteria against which preservation may be tested; validation against
these Information Properties would be a necessary, although not always sufficient,
condition for testing the adequacy of the preservation activity.
12.3 Migration/Transformation
At some point it may be decided that maintaining the original medium or the
Representation Network for a digital object is not practical for cost reasons, or does
not meet requirements for some other reason. Therefore the digitally encoded infor-
mation must be encoded in some other way, either the same bit sequences on new
media or else changed bit sequences.
It is possible to identify four primary digital Migration types. The primary types,
ordered by increasing risk of information loss, are:
1. Operations which do not change the bit sequences
•
Refreshment
: A Digital Migration where a media instance, holding one or
more AIPs or parts of AIPs, is replaced by a media instance of the same
type by copying the bits on the medium used to hold AIPs and to manage
and access the medium. As a result, the existing Archival Storage mapping
infrastructure, without alteration, is able to continue to locate and access
the AIP.
◦
As discussed at the start of the topic many processes go on to translate from
magnetic domains (for a magnetic disk) to bits. This bit copy may not be a
physical copy.
•
Replication
: A Digital Migration where there is no change to the Packaging
Information, the Content Information and the PDI. The bits used to convey
these information objects are preserved in the transfer to the same or new
