AI - a Guide to Intelligent Systems.pdf - Member of EEPIS

INTERACTION OF FRAMES AND RULES
147
Figure 5.10
The Credit Evaluation class, WHEN CHANGED and WHEN NEEDED methods
Suppose we want to evaluate the credit request selected by the user. The
expert system is expected to begin the evaluation when the user clicks the
Evaluate Credit pushbutton on the input display. This pushbutton is attached to
the attribute Evaluate Credit of the class Credit Evaluation shown in Figure 5.10.
The attribute Evaluate Credit has the WHEN CHANGED method attached to it,
and when we select the Evaluate Credit pushbutton at run time, the attribute
Evaluate Credit receives a new value, a value of TRUE. This change causes the
WHEN CHANGED method to execute. The PURSUE command tells Level5 Object
to establish the value of the attribute Evaluation of the class Credit Evaluation. A
simple set of rules shown in Figure 5.11 is used to determine the attribute’s value.
How does the inference engine work here?
Based on the goal, Evaluation OF Credit Evaluation, the inference engine finds
those rules whose consequents contain the goal of interest and examines them
one at a time in the order in which they appear in the rule base. That is,
the inference engine starts with RULE 9 and attempts to establish whether the
attribute Evaluation receives the Give credit value. This is done by examining
the validity of each antecedent of the rule. In other words, the inference engine
attempts to determine first whether the attribute Collateral has the value of
Excellent, and next whether the attribute Financial rating is Excellent. To determine
whether Collateral OF Credit Evaluation is Excellent, the inference engine
examines RULE 1 and RULE 2, and to determine whether Financial rating OF
Credit Evaluation is Excellent, it looks at RULE 8. If all of the rule antecedents are
valid, then the inference engine will conclude that Evaluation OF Credit Evaluation
is Give credit. However, if any of the antecedents are invalid, then the
conclusion is invalid. In this case, the inference engine will examine the next
rule, RULE 10, which can establish a value for the attribute Evaluation.