Preset Two-head Automata and Morphological Analysis of Natural Language*

Modeling the morphological structure of natural languages in terms of a nondeterministic finite-state automaton is shown to be inadequate in its handling of some common natural language phenomena. We show that a two-tape nondeterministic automaton is capable of handling these phenomena. The modeling is improved by the specification of a new type of automaton, the preset two-head automaton, which we argue is equivalent in expressive power to a linear context-free grammar. We discuss the operation of a parser which implements the improved model.