Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

Rule 1: If On (X, Y)
Clear (X)
Clear (Z)
Add List: On (X, Z)
Clear (Y)
Delete List: On (X,Y)
Clear (X)
Rule 2: If On (X,Y)
Clear (X)
Add List: On (X, Table)
Clear (Y)
Delete List: On (X, Y)
Rule 3: If On (X, Table)
Clear (X)
Clear (Z)
Add List: On(X, Z)
Delete List: Clear (Z)
On (X, Table)
We can try to solve the above problem by the following sequencing of
operators. Rule 2 is applied to the initial problem state with an instantiation of X
=A and Y =B to generate state S1 (fig. 12.4). Then we apply Rule 3 with an
instantiation of X =B and Z =A to generate state S2. Next Rule 3 is applied once
again to state S2 with an instantiation of X =C and Z =B to yield the goal state.
Generating the goal from the given initial state by application of a sequence of
operators causes expansion of many intermediate states. So, forward reasoning is
not appropriate for such problems. Let us try to explore the problem through
backward reasoning.
12.2.1 Planning by Backward Reasoning
Much effort can be saved, if we generate a plan for the current problem by
backward reasoning. While planning through backward reasoning, we should
check the required preconditions to satisfy a given goal. Further, to satisfy
new sub-goals generated, we should check the existence of their preconditions
in the ADD-list of rules, which on firing generate the sub-goals. To illustrate