17_Planning

17_Planning - Challenge TELL(KB Knows(John,Jim ASK(KB...

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11/16/2009 1 Planning Challenge TELL(KB, Knows(John,Jim)) ASK(KB, Hates(John, Jim)) ASK(KB, Hates(John, x)) Want a way to automatically find path to a goal How to achieve “ Hates(John, Jim)”? Planning A planning agent will construct plans to achieve its goals, and then execute them. Analyze a situation in which it finds itself and develop a strategy for achieving the agent’s goal. Achieving a goal requires finding a sequence of actions that can be expected to have the desired outcome. Problem Solving Representation of actions actions generate successor states Representation of states all state representations are complete Representation of goals contained in goal test and heuristic function Representation of plans unbroken sequence of actions leading from initial to goal state Planning Example GOAL: Get a quart of milk and a bunch of bananas and a variable-speed cordless drill. Planning vs. Problem Solving 1. Open up the representation of states, goals and actions. •S t a t e s and goals represented by sets of sentences – Have ( Milk ) At i td b l th t t th i Actions represented by rules that represent their preconditions and effects: Buy ( x ) achieves Have ( x ) and leaves everything else unchanged This allows the planner to make direct connections between states and actions.
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11/16/2009 2 Planning vs. Problem Solving 2. Most parts of the world are independent of most other parts. •C a n solve using divide and conquer strategy. a n re use sub plans (go to supermarket) Assumes partial decomposability Assumption fails if cost of combination is too high Planning vs. Problem Solving 3. Planner is free to add actions to the plan wherever they are needed, rather than in an incremental sequence starting at the initial state state. •N o connection between the order of planning and the order of execution. Representation of states as sets of logical sentences makes this freedom possible. Efficient ordering – reduce branching Planning as a Logical Inference Problem Axioms: On(A,C) On(C,Table), On(D,B), On(B,Table), Clear(A), Clear(D) Plus rules for moving things around… Prove: On (A,B) On(B,C) Planning as Deduction: Situation Calculus In first order logic, once a statement is shown to be true, it remains true forever. Situation calculus: way to describe change in first order logic. first order logic.
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This note was uploaded on 05/30/2010 for the course CS 4700 taught by Professor Joachims during the Fall '07 term at Cornell.

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17_Planning - Challenge TELL(KB Knows(John,Jim ASK(KB...

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