tailieunhanh - Báo cáo khoa học: "Nonconcatenative Finite-State Morphology"

In the last few years, so called morphology, in general, and two-level morphology in particular, have become widely accepted as paradigms for the computational treatment of morphology. Finite-state morphology appeals to the notion of a finite-state transducer, which is simply a classical finite-state automaton whose transitions are labeled with pairs, rather than with single symbols. The automaton operates on a pair of tapes and advances over a given transition if the current symbols on the tapes match the pair on the transition. . | Nonconcatenative Finite-State Morphology by Martin Kay Xerox Palo Alto Research Center 3333 Coyote Hill Road Palo Alto CA 94304. USA In the last few years so called ĩnừe-staíe morphology in general and two-level morphology in particular have become widely accepted as paradigms for the computational treatment of morphology. Finite-state morphology appeals to the notion of a finite-state transducer which is simply a classical finite-state automaton whose transitions are labeled with pairs rather than with single symbols. The automaton operates on a pair of tapes and advances over a given transition if the current symbols on the tapes match the pair on the transition. One member of the pair of symbols on a transition can be the designated null symbol which we will write . When this appears the corresponding tape is not examined and it does not advance as the machine moves to the next state. Finite-state morphology originally arose out of a desire to provide ways of analyzing surface forms using grammars expressed in terms of systems of ordered rewriting rules. Kaplan and Kay in preparation observed that finite-state transducers could be used to mimic a large class of rewriting rules possibly including all those required for phonology. The importance of this came from two considerations. First transducers are indifferent as to the direction in which they are applied. In other words they can be used with equal facility to translate between tapes in either direction to accept or reject pairs of tapes or to generate pairs of tapes. Second a pair of transducers with one tape in common is equivalent to a single transducer operating on the remaining pair of tapes. A simple algorithm exists for constructing the transition diagram for this composite machine given those of the origi nal pair. By repeated application of this algorithm it is therefore possible to reduce a cascade of transducers each linked to the next by a common tape to a single transducer which accepts exactly