17 Mar 2005
CS 3243 - Logical Inference
24
Forward and
backward chaining
nHorn Form (restricted)
KB = conjunction of Horn
clauses
nHorn clause =
nproposition symbol;
or
n(conjunction of symbols) Þ symbol
nE.g., C Ù (B Þ A) Ù (C Ù D Þ B)
nModus Ponens (for Horn Form): complete for Horn KBs
α1, … ,αn, α1 Ù … Ù αn Þ β
β
nCan be used with forward chaining or backward chaining.
nThese algorithms are very natural and run in linear
time
