Information Technology Reference
In-Depth Information
Common ways of preserving such differences for text files such as computer
source code, use the diff [
24
] format to store the changes between one version
and the next. Thus the original plus the incremental diff files would be stored
and to reproduce the file at any particular point the appropriate diffs would
be applied. Regarding the collection of the initial plus the diffs as the digital
object being preserved, the Representation Information needed to construct the
object at any point is therefore the definition of the diff format plus the naming
convention which specifies the order in which the diffs are applied.
Another trivial example would be where essentially the only change allowed
is to append additional material to the end of the digital object. The recording
of Provenance is often an example of this. One common way of recording when
the addition was made, and of delimiting the addition, is to add a time-tag. The
Representation Information needed here, in addition to that needed to under-
stand the material itself, is the description of the meaning of the time tag - what
format, what timezone, does it tag the material which comes after it or before it?
7.7.7 Active
7.7.7.1 Actions and Processes
Some information has, as an integral part of its content, an implicit or explicit pro-
cess associated with it. This could be argued to be a type of semantics, however
it is probably sufficiently different to need special classification. Examples of this
include databases or other time dependent or reactive systems such as Neural Nets.
The process may be implicitly encoded in the data, for example with the scheme
for encoding time dependence in XML data as noted above. Alternatively the pro-
cess may be held in the Representation Information - possibly as software. Amongst
many other possibilities under this topic, Software and Software Emulation are
among the most interesting [
68
]. Emulation is discussed in more detail in Sect.
7.9
.
However an important limitation is that one is “stuck in time” in that one can
do what was done before but one cannot immediately use the digital object in new
ways and with other tools, for example newer analysis packages.
For other processes and activities text documentation, including source code, can,
and is, created. In general such things are difficult to describe in ways which support
automation. However these things are outside the remit of this topic and will not be
described further here.
7.7.8 Passive
The other digital objects described above, apart from those explicitly marked as
“active” are “passive”.
