Inference in first-order logic

3 Mar 2004

CS3243 - Inference

Logic programming: Prolog

lAlgorithm = Logic + Control

lBasis: backward chaining with Horn clauses + bells & whistles

Widely used in Europe, Japan (basis of 5th Generation project)

Compilation techniques Þ 60 million LIPS

lProgram = set of clauses = head :- literal1, … literaln.

criminal(X) :- american(X), weapon(Y), sells(X,Y,Z), hostile(Z).

lDepth-first, left-to-right backward chaining

lBuilt-in predicates for arithmetic etc., e.g., X is Y*Z+3

lBuilt-in predicates that have side effects (e.g., input and output

lpredicates, assert/retract predicates)

lClosed-world assumption ("negation as failure")

¡e.g., given alive(X) :- not dead(X).

¡alive(joe) succeeds if dead(joe) fails