Information Technology Reference
In-Depth Information
boundary between Simple Objects and Composite Objects is not sharp. For example
a Tree-type object where the leave nodes are not primitive types may be consid-
ered a Composite Object; the Multivalent Browser document model may be rather
complex. Nevertheless it is worth maintaining the distinction between
Simple Objects, where we have some chance of being able to do something sen-
sible with the information content using widely applicable, reasonably standard,
interfaces - display, search, process etc.
and
Composite Objects, which are likely to require a number of additional steps
to unpack the individual Simple Objects - however the difficulty is then that
the relationship between those Simple Objects has to be defined elsewhere.
Usually creators of Composite Objects embed the knowledge of those relation-
ships within associated software. These relationships may be captured using
Knowledge Management techniques.
7.8.3.1 On-demand Objects
In the process of managing objects and creating, for example, DIPs, there is a need to
create objects “on-the-fly”. One can in fact regard on-demand as the norm, depend-
ing on the level of detail at which one looks at the systems; there are many processes
hidden from view in the various hardware and software systems.
Of more immediate interest are processes and workflows which act on the data
objects to produce some desired output. There are a variety of workflow description
languages and types of process. The virtualisation required here is an abstract layer
which can accommodate several different underlying workflow systems. This level
of abstraction is outside the scope of this topic and will not be covered here.
7.8.4 Discipline Specific Information Virtualisation
As noted above, each of the common virtualisations in the previous section is useful
because one can rely on some (simple) specific behaviour from each type. Although
simple, the behaviours can be combined to produce quite complex results. However
different disciplines can produce a number of specialised types of, for example,
images. By this is meant that a number of additional, specialised, behaviours become
available for each specialised type. Expanding in Fig. 7.16 ,Fig. 7.21 shows some
further examples of specialisations of image types. The Astronomical image will
add the functionality of, for example, a World Coordinate System i.e. the Right
Ascension/Declination of object at the centre of the image, and the direction and
angular size on the sky of each pixel in the image. The set of FITS image standards
provide the basis of this type of additional functionality. Astronomical images can
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