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Fig. 4.4 Dimensions of abstracting to a representation. (The diagram illustrates the emphasis of
the two main software engineering methods on process (vertical axis) and information (horizontal
axis). Any model of knowledge can be represented at some level of abstraction as a point in this
space. The scales of abstraction indicate the order that each method (enclosed in an oval ) is used to
implement a system.)
The advantage of these approaches is that each can provide a method: an explicit
procedure that ensures a reliable design that can be justified. However, these meth-
ods are appropriate only for the imperative programming of data. Because of their
influence, there is a tendency for knowledge analysts to bifurcate knowledge into
(see Fig. 4.5 ) taxonomic structures (suitable for storage) and processes (appropriate
for imperative programming), as a matter of course.
However, as D. Michie pointed out, people do not naturally conceive their own
knowledge in either of these extreme forms of data and processing. Representation
of people's knowledge is best understood in terms of some intermediate form that
combines data and rule. Many practical skills use such a mixture: navigators, statis-
ticians, architects and electronic engineers all use tables as well as rules. Michie
called this intermediate form “the human window” (Michie 1979 ). It is the shaded
area in Fig. 4.5 . Interactive systems—whether used by experts or by novices—should
operate within these limits.
The diagram (Fig. 4.5 ) implies that knowledge can be considered as something
apart from its representation. The same knowledge can thus be described in different
forms in the same way that music can be represented as the physical undulations on
a disc, or the magnetic orientations on tape, or the musical notations on paper. The
inverse relationship between process and data for a single source of knowledge is also
illustrated here. The curved line indicates the many different mixes of data and pro-
cess. The spheres denote a single source of knowledge represented in different ways
(Addis 1980 ). Michie's 'Human Window' is labelled as the 'Area of Conception'.
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