Information Technology Reference
In-Depth Information
in which the Content Data Object may be used. One advantage of leaving the bit
sequences unchanged is that evidence of Authenticity is more easily sustained.
Alternatively the object may be changed into one that can be processed with
contemporary access and use mechanisms. This is referred to in OAIS as a
Transformation, a type of Migration, which is discussed below. There are impli-
cations for Authenticity which are discussed in
Chap. 13
, particularly
Sect. 13.6.2
.
The following matrix shows the various combinations of these alternatives.
Content data object unchanged
Content data object changed
Access service
unchanged
If using the original software
executable: emulation
If using the original source code:
rebuild executable
Re-implement access service
Access service
changed
Implement new access services based
on the representation information
describing original content data
object
Implement new access services
based on the representation
describing the new content data
object
12.1 Description - Adding Representation Information
As should be clear from the discussion in earlier chapters it is necessary to maintain
the Representation Network so that it is adequate for a member of the Designated
Community to continue to understand and use the digital object. However things
change over time and so the Representation Network must be altered appropriately.
In order to do this the techniques extensively discussed in
Chap. 8
to identify any potential gaps in the Representation Network can be
used. Practical ways of doing this are described in detail in
Chap. 16
and illustrated in Part II.
This approach allows the greatest flexibility because one has the ability to dis-
cover entirely new ways of looking at the digital objects, however whilst it can be
the most rewarding, it can also be the most difficult.
12.2 Maintaining Access
An alternative to using description is to maintain the “current” ways of accessing the
digital object, and OAIS discusses several ways of doing this. One can think of this
in terms of interfaces, either programmatic or user interfaces. In addition hardware
emulation can be viewed as doing essentially the same thing but this deserves the
more extensive discussion given in
Sect. 7.9
, although another type of emulation is
described below.
