1. CPSC 433 Artificial Intelligence Rule Based Systems (Prolog) M. Reza Zakerinasab mrzakeri@ucalgary.ca Please include [CPSC433] in the subject line of any emails regarding this course. Slides originally created by Andrew M Kuipers. Some slides adopted from 600.325/425 Declarative Methods - J. Eisner

2. 2 Prolog as constraint programming An ordinary constraint between two variables: Person and Food Prolog makes you name this constraint. Here’s a program that defines it: –eats(sam, dal).eats(josie, samosas). –eats(sam, curry).eats(josie, curry). –eats(rajiv, dal). … Now it acts like a subroutine! At the Prolog prompt you can type –eats(Person1, Food1). % constraint over two variables –eats(Person2, Food2). % constraint over two other variables (Person, Food) PersonFood samdal samcurry josiesamosas josiecurry rajivdal CPSC 433 Artificial Intelligence

3. 3 Using Prolog –eats(sam, dal).eats(josie, samosas). –eats(sam, curry).eats(josie, curry). –eats(rajiv, burgers).eats(rajiv, dal). … –eats(Person1, Food), eats(Person2, Food). Person1=sam, Person2=josie, Food=curry Person1=josie, Person2=sam, Food=curry … Your program file (compiled) Sometimes called the “database” “Query” that you type interactively Prolog’s answer CPSC 433 Artificial Intelligence

4. Adding more rules… eats(sam, dal).eats(josie, samosas). eats(sam, curry).eats(josie, curry). eats(rajiv, burgers).eats(rajiv, dal). compatible(Person1, Person2) :- eats(Person1, Food), eats(Person2, Food). compatible(Person1, Person2) :- watches(Person1, Movie), watches(Person2, Movie). compatible(hal, Person2) :- female(Person2), rich(Person2).

5. CPSC 433 Artificial Intelligence Basic Prolog Process Negate query, set as current goal. while current goal is non-empty: choose the leftmost subgoal if a rule applies to the subgoal: select the first applicable rule (top-to-bottom) perform resolution on subgoal and selected rule else: backtrack if possible, otherwise fail success

6. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). Logically sound?!! ?- witch(X). Goals

7. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)

8. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)

9. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)

10. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)

11. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)

12. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)

13. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(_G0)

14. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(_G0)

15. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(duck)

16. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(duck)

17. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(duck)   woman(duck)

18. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(duck)   woman(duck) fail! backtrack...

19. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(_G0)

20. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(_G0)  floats(_G1)   sameweight(_G1, _G0)

21. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(_G0)  floats(_G1)   sameweight(_G1, _G0)

22. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(_G0)  floats(duck)   sameweight(duck, _G0)

23. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(_G0)  floats(duck)   sameweight(duck, _G0)

24. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(_G0)  floats(duck)   sameweight(duck, girl)

25. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(_G0)  floats(girl)

26. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(_G0)   woman(_G0)  madeofwood(girl)

27. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(girl)   woman(girl)

28. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(_G0)  burns(girl)   woman(girl) works this time

29. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). Goals  witch(girl)

30. CPSC 433 Artificial Intelligence Sir Bedevere’s Infamous Deduction witch(X) :- burns(X),woman(X). woman(girl). burns(X) :- madeofwood(X). madeofwood(X) :- floats(X). floats(duck). floats(Y) :- floats(X),sameweight(X,Y). sameweight(duck,girl). ?- witch(X). X = girl