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Bài giảng Trí tuệ nhân tạo - Chapter 6: Using rules

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Using Rules  
Chapter 6  
Logic Programming  
(Definite) logic program:  
A ← B1, B2, …, Bm  
head body  
program clause (Horn)  
← A1, A2, …, An  
goal clause  
2
Logic Programming  
PROLOG (Alain Colmerauer 1972):  
apartmentpet(X) :- pet(X), small(X)  
pet(X) :- cat(X)  
pet(X) :- dog(X)  
dog(X) :- poodle(X)  
small(X) :- poodle(X)  
poodle(fluffy)  
pet(mittens)  
?- apartmentpet(X)  
3
Forward vs. Backward Reasoning  
• Forward: from the start states.  
• Backward: from the goal states.  
4
Forward vs. Backward Reasoning  
• Forward rules: to encode knowledge about how to  
respond to certain input.  
• Backward rules: to encode knowledge about how to  
achieve particular goals.  
5
Forward vs. Backward Reasoning  
Combining forward and backward reasoning  
← A1, …, Ak-1, Ak, Ak+1, …, An  
achieved by  
forward reasoning  
achieved by  
backward reasoning  
6
Production Systems  
Working memory:  
{A(1), A(2), B(2), B(3), B(4), C(5)}  
Rule memory:  
A(x) ∧ B(x) ∧ C(y) ⇒ add D(x)  
A(x) ∧ B(y) ∧ D(x) ⇒ add E(x)  
A(x) ∧ B(x) ∧ E(x) ⇒ delete A(x)  
7
Production Systems  
RETE network (Forgy, 1982)  
D
A=D  
C
add E  
add D  
B
A=B  
A
C(5)  
D(2)  
A(1), A(2)  
B(2), B(3), B(4)  
A(2)  
B(2)  
E
delete A  
8
Production Systems  
Conflict resolution:  
Preferences based on rules:  
Specificity of rules  
Physical order of rules  
Preferences based on objects:  
Importance of objects  
Position of objects  
Preferences based on states:  
Evaluation of states  
9
Pattern Matching  
ELIZA (Weizenbaum, 1966):  
Person: Men all are alike.  
ELIZA: In what way?  
Person: They're always bugging us about something or other.  
ELIZA: Can you think of specific example?  
Person: Well, my boyfriend made me come here.  
ELIZA: Your boyfriend made you come here.  
Person: He says I'm depressed much of the time.  
ELIZA: I am sorry to hear you are depressed.  
Person: It's true. I am unhappy.  
ELIZA: Do you think coming here will help you not to be unhappy?  
10  
Pattern Matching  
ELIZA (Weizenbaum, 1966):  
Person: I need some help, that much seems certain.  
ELIZA: What would it mean to you if you got some help?  
Person: Perhaps I could learn to get along with my brother.  
ELIZA: Tell me more about your family.  
....  
11  
Pattern Matching  
ELIZA (Weizenbaum, 1966):  
(X me Y)  
→ (X you Y)  
(I remember X)  
→ (Why do you remember X just now?)  
(My {family-member} is Y) → (Who else in your family is Y?)  
(X {family-member} Y)  
....  
→ (Tell me more about your family)  
Person: My brother is mean to me.  
ELIZA: Who else in your family is mean to you?  
....  
12  
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