Chap.13 Planning and Acting

CS570 Artificial Intelligence

Kwang-hyung Lee

13.1 Conditional Planning

• Contingency planning : incomplete planning by constructing a conditional plan that accounts for each possible situation

• Sensing action:The agent includes sensing actions to find which part of the plan to be execute

13.1 Conditional Planning

• Ex) “Fixing a flat tire”(1) Possible operators

• Op(ACTION:Remove(x),PRECOND:On(x),EFFECT:Off(x) ClearHub(x) On(x))

• Op(ACTION:PutOn(x),PRECOND:Off(x) ClearHub(x),EFFECT:On(x) ClearHub(x) Off(x))

• Op(ACTION:Inflate(x),PRECOND:Intact(x) Flat(x),EFFECT:Inflated(x) Flat(x))

(2) goal• On(x) Inflated(x)

(3) Initial conditions• Inflated(Spare) Intact(Spare) Off(Spare) On(Tire1) Flat

(Tire1)

13.1 Conditional Planning

(4) Initial plan• [Remove(Tire1), PutOn(Spare)]

• The initial plan is good if there is no Intact(Tire1). But, if Tire1 is intact, only the inflation is needed

• Conditional stepIf(<condition>,<ThenPart>,<ElsePart>,)

• If(Intact(Tire1),[Inflate(Tire1)],[Remove(Tire1),PutOn(Space)])

• Sensing Actionx,s Tire(x) KnowsWhether(“Intact(x)”,Result(CheckTire(x),

s))

In our action schema format• Op(ACTION:CheckTire(x),

PRECOND:Tire(x),EFFECT:KnowsWhether(“Intact(x)”))

13.1 Conditional Planning

13.1 Conditional Planning

• An algorithm for generating conditional plans– ex) Example:”Fixing a flat tire”

• Context :Contexts of steps are essential for keeping track of which steps can establish or violate the preconditions

13.1 Conditional Planning

• Two open conditions to be resolved– On(x)

– Inflated(x)

• Introduce operator– Inflate(Tire1)

– preconditions Flat(Tire1) and Intact(Tire1)

13.1 Conditional Planning

• Precondition Intact(Tire1) ?– There is no action that can make it satisfied

• But the action CheckTire(x) allows us to know the truth value of the preconditon conditional step : Sensing action

• We add the CheckTime step to the plan with a conditional link :dotted arrow

13.1 Conditional Planning

• We add steps for the case where Tire1 is not intact: another Finish action

13.1 Conditional Planning

• If we add Inflate(Tire1) to the new Finish step, the precondition Intact(Tire1) is inconsistent with Intact(Tire1). Therefore, we link the start step to Inflated step Context is useful, here.

13.1 Conditional Planning

• We add Remove(Tire1), PutOn(Spare) to satisfy the condition On(Spare)

• But, the Remove(Tire1) can threaten the causal link protecting On(Tire1)

• We resolve the threat by conditioning the step so that its context becomes incompatible with the context of precondition it is threatening.In the example, CheckTire can give Intact(Tire1)

• If we link from CheckTire to Remove(Tire1), then the Remove is no longer a threat

13.1 Conditional Planning

13.1 Conditional Planning

13.1 Conditional Planning