flex Expert System Toolkit - LPIS

Appendix A - Examples 166
Appendix A - Examples
This appendix includes two examples used to illustrate some of the
techniques involved in writing flex programs.
Example 1 is an animal taxonomy, which is used to demonstrate some of
the features of the frame system of flex.
Example 2 is a forward chaining solution to the Water Jugs problem, which
demonstrates the use of rule transition networks to update the rule agenda
used in forward chaining.
Example 1 - Analysing a Taxonomy
The purpose of this example is to illustrate most of the concepts within the
frame sub-system of flex. This involves the representation (using constructs
from the Knowledge Specification Language) of a taxonomy for the animal
kingdom, together with an algorithm for identifying species. We then give a
couple of example questions that can be posed.
As in the rest of this manual, in the following examples the KSL keywords
are emboldened for clarity (they should not be distinguished in source texts).
The Animal Kingdom
The animal kingdom can be split into three main groups, namely mammal,
fish and bird. Each of these main groups has its own set of characteristics
which separate it from the others. The following KSL statements describe
this frame hierarchy, together with the associated default values.
frame animal
default blood is warm .
frame mammal is an animal
default skin is fur and
default habitat is the land and
default motions are walk .
frame fish is an animal
default skin is scale and
default habitat is water and
default motions are { swim } and
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flex toolkit