CS451CS551EE565 ARTIFICIAL INTELLIGENCE

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CS451/CS551/EE565ARTIFICIAL INTELLIGENCE

• Deductive reasoning in FOL
• 10-20-2006
• Prof. Janice T. Searleman
• jets_at_clarkson.edu, jetsza

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Outline

• Deductive reasoning
• Unification matching, mgu
• Skolemizing
• Forward Backward Chaining
• Reading Assignment AIMA
• Chapter 9 Inference in FOL
• HW5 due Wednesday, 10/25/06
• Project proposal due Friday, 10/27/06

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Notes done in class

• deductive reasoning
• examples of unification
• var lt- constant
• var lt- another var (renaming)
• var lt- function (not involving the same var)
• occurs check
• common errors
• examples of skolemizing
• most general unifier

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Recap Unification

• process of matching expressions and finding a
  unifier (substitution) that makes the two
  expressions identical
• Unify(a,ß) ? if a? ß?
• p q ?
• Knows(John,x) Knows(John,Jane)
• Knows(John,x) Knows(y,OJ)
• Knows(John,x) Knows(y,Mom(y))
• Knows(John,x) Knows(x,OJ)
• Standardizing apart eliminates overlap of
  variables, e.g., Knows(z17,OJ)

x/Jane
x/OJ,y/John
y/John,x/Mom(John)
fail
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Unification

• To unify Knows(John,x) and Knows(y,z),
• ? y/John, x/z or ? y/John, x/John,
  z/John
• The first unifier is more general than the
  second.
• There is a single most general unifier (MGU) that
  is unique up to renaming of variables.
• MGU y/John, x/z

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The unification algorithm
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The unification algorithm
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Generalized Modus Ponens (GMP)

• p1', p2', , pn', ( p1 ? p2 ? ? pn ?q)
• q?
• p1' is King(John) p1 is King(x)
• p2' is Greedy(y) p2 is Greedy(x)
• ? is x/John,y/John q is Evil(x)
• q ? is Evil(John)
• GMP used with KB of definite clauses (exactly one
  positive literal)
• All variables assumed universally quantified

where pi'? pi ? for all i
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Intelligent Answering Service

• Mr. Coleman wishes to call his wife. Her
  answering service tells him that his wife, Dr.
  Coleman, is visiting Dr. Gordon and that Dr.
  Gordon is at patient Wagners residence.

What kind of agent would you choose for the
intelligent answering service, and why?