FINITE-STATE UNIFICATION AUTOMATA AND RELATIONAL LANGUAGES

We define the new notion of a (finite-state) unification automaton, a device for finite-state recognition of relational languages by means of unification transitions. Words in such a language are formed by composing base relations, and have the general form r(i1)(x(j1), x(k1))...r(in)(x(jn), x(kn)) for some n. Generation of such languages by regarding Horn clauses as grammers has been considered before, but to the best of our knowledge, recognizing such languages by suitably designed automata is a new approach. The main result presented is a pumping lemma, forming a necessary condition for finite-state recognizability. Some example results about such automata are given. (C) 1994 Academic Press, Inc.