PowerPoint Presentation
Introduction to AI
-Tutorial Logic for KRR –
Francesca Toni
Colonel West again
Criminal(x) ← American(x), Weapon(y), Sells(x, y, z), Hostile(z)
Owns(Nono,M1)
Missile(M1)
Sells(West, x,Nono) ← Owns(Nono, x),Missile(x)
American(West)
Weapon(x) ← Missile(x)
Hostile(x) ← Enemy(x,America)
Enemy(Nono,America)
2
1) Compute using SLD resolution all possible answers for the query (∃x) Criminal(x)
2) Give the minimal Herbrand model of this set of definite clauses
3) Let S be the set of all these clauses. Determine TS↑
1 , TS↑
2and TS↑
3
and the least fixed point of TS
Search for solutions by SLD resolution
Admires(Ann, Bob) Admires(Ann, Carla) Admires(x,y) ←
Lecturer(x), Lecturer(y)
Lecturer(Ann) Lecturer(Dave) Lecturer(Eric)
Rich(Carla) Rich(Eric) Rich(Ann) ← Rich(Carla)
Which rich person does Ann admire?
Formulate this query and compute all possible answers obtainable by
SLD resolution, using depth-first search with backtracking. Show all
failed attempts explicitly.
More on search for solutions by SLD resolution
Consider the set of definite clauses (written using logic programming
notation: variables start with capital letters)
S ={ p(X) ← q(X,Y), r(Y), q(2,3) ←, q(2,4) ←, r(4) ← , r(3) ← r(3) }
and query p(X). Apply 1 step of SLD resolution to obtain q(X,Y), r(Y):
1) Does it matter in which order q(X,Y) and r(Y) are selected for
determining an answer?
2) Does it matter in which order clauses are chosen for determining an
answer?