artificial-intelligencerule-enginefirst-order-logicrete

Are function symbols allowed in rule engines / Rete algorithm?

AI: A Modern Approach brings up the Rete algorithm when discussing inference in first-order logic.

However, all descriptions of the Rete algorithm I found seem to use rules free of function symbols. In other words, rules look like

a(X) ∧ b(X, Y) → c(Y)

but not

a(f(X)) ∧ b(X, Y) → c(f(Y))

(The difference can be fundamental, as it is the difference between Prolog and Datalog, only one of which is Turing-complete)

Is the Rete algorithm limited to rules free of function symbols? Do modern rule engines like Drools and CLIPS handle function symbols?

Solution

  • In CLIPS, this is how you'd implement the rule "For every person, there exists one and only one father of said person, and if a person's father is rich, then so is he/she":

    (defrule inherited-wealth
   (forall (person ?p)
           (father ?p ?f)
           (not (father ?p ~?f)))
   (person ?p)
   (father ?p ?f)
   (rich ?f)
   =>
   (assert (rich ?p)))