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

plan is an order of partially planned operators. The partially ordered plans for
the problem of fig. 12.10 are listed below:
{G1, G2, G3, G4, G5}
{G1, G3, G2, G4, G5} and
{G1, G3, G4, G2, G5}
We now have to select which of the above three partially ordered plans
leads to a complete plan for the goal or the sub-goal. So, in the least
commitment planning we first search in the space of partially ordered plans
and then select the correct complete plan among those plans.
12.3.2 Realizing Least Commitment Plans
For realizing a least commitment plan we require one or more of the following
operations [6]:
a) Step Addition: This stands for the generation of a partially
ordered plan for one sub-goal.
b) Promotion: This constrains one step to come before another in
a partially ordered plan.
c) Declobbering: Suppose state S1 negated (deleted) some precondition
of state S3. So, add S2 such that S2 follows S1 and
S3 follows S2, where S2 reasserts the negated pre-conditions of
S3.
d) Simple Assignment: Instantiate a variable to ensure precondition
of a step.
e) Separation: Instantiation of variables is sometimes not done
intentionally to keep the size of the plan manageable.
The following example of the well-known ‘blocks world’ problem,
discussed earlier, will best illustrate the above definitions. Remember the
problem was enlisted as follows:
Given: On (A,B) ∧ Clear ( C) ∧ Clear(A) ∧ On(C, Table) ∧ On(B, Table).
Find a plan for: On (B, A) ∧ On(C, B).