Lecture 5 - Logical Agents Chapter 7 Knowledge bases...

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Logical Agents Chapter 7
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Knowledge bases Knowledge base (KB): set of sentences in a formal language Inference: deriving new sentences from the KB. E.g.: A>5, B>A, B>5 Two blind persons, each bought 2 pairs of black socks and 2 pairs of white socks. Unfortunately, they mixed up the eight pairs. All pairs are in their original packages. How can they get 2 pairs of black socks and 2 pairs of white socks?
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Wumpus World PEAS description Performance measure gold +1000, death -1000 -1 per step, -10 for using the arrow Environment Squares adjacent to wumpus are smelly Squares adjacent to pit are breezy Glitter iff gold is in the same square Shooting kills wumpus if you are facing it Shooting uses up the only arrow Grabbing picks up gold if in same square Releasing drops the gold in same square Sensors: Stench, Breeze, Glitter, Bump, Scream, Bump Actuators: Left turn, Right turn, Forward, Grab, Release, Shoot
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Wumpus world characterization Fully Observable No – only local perception Deterministic Yes – outcomes exactly specified Static Yes – Wumpus and Pits do not move Discrete Yes Single-agent? Yes – Wumpus is essentially a natural feature
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Exploring a wumpus world
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Exploring a wumpus world
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Exploring a wumpus world
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Exploring a wumpus world
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Exploring a wumpus world
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Exploring a wumpus world
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Exploring a wumpus world
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Exploring a wumpus world
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Logic in general Logics are formal languages for representing information such that conclusions can be drawn Syntax defines the sentences in the language Semantics define the "meaning" of sentences; i.e., define truth of a sentence in a world E.g., the language of arithmetic x+2 ≥ y is a sentence; x2+y > {} is not a sentence x+2 ≥ y is true iff the number x+2 is no less than the number y Possible worlds (i.e. models) x+2 ≥ y is true in a world where x = 7, y = 1 x+2 ≥ y is false in a world where x = 0, y = 6
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Entailment Entailment means that one thing follows from another: KB ╞ α Knowledge base KB entails sentence α if and only if α is true in all worlds where KB is true E.g., x+y = 4 entails 4 = x+y
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Entailment in the wumpus world Situation after detecting nothing in [1,1], moving right, breeze in [2,1] Consider possible models for KB assuming only pits 3 Boolean choices 8 possible models
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Lecture 5 - Logical Agents Chapter 7 Knowledge bases...

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