人工智能和神经网络AI-NN-05-01,06.ppt

E.g., C D A A ? B B B G E G A C Fact: A ? B Rules: A ? C ? D B ? E ? G Goal: C ? G Rule Matching Goal Matching (C) Rule Application in Predicate Logic Fact and rule expressions are the same as above: -- Variables are universally quantified; -- Any existentially variables are already Skolemized. Goal wffs, however, is dual to those above: -- Universal variables are replaced by Skolem functions; -- Existential quantifiers in the Skolemized goal wff can then be dropped; -- Variables remaining in goal wffs have been renamed so that the same variable does not occur in more than one disjunct of the goal wff. Rule Application -- A rule is applicable if the AND/OR graph contains a literal node L’ that unifies with L by mgu, u; -- Application of this rule, then, extends this graph by creating a match arc directed from the node L’ to a new descendant node L; -- This descendant node L is the root node of the graph representation of Wu; -- Label the match arc by the mgu, u. L’ L Wu u Rule Fact Goal Match E.g., P(x, y) ? [Q(x,A) ? R(B,y)] P(x, y) X(B) S(A) P(A,B) R(B,y) Q(x,A) Q(x,A) ? R(B,y) Fact wff Rule wff: P(A,B) ? S(A) ? X(B) {A/x, B/y} Rule Match The clauses corresponding to these solution graphs are: S(A) ? X(B) ? Q(A,A) A/x S(A) ? X(B) ? Q(B,B) B/y Rule Application Important Remarks: -- Any solution graph (terminating in literal nodes) can have more than one match arc. -- In computing the set of clauses represented by AND/ OR graph containing several match arcs, only those solution graphs terminating in literal nodes having consistent match arc substitutions are counted. -- The clause represented by a consistent solution graph is obtained by applying a special solution, called the unifying composition, to the disjunction of the literals labeling its terminal nodes. -- The definition of consistent substitutions: Given a set of substitutions, {u