@MISC{Ritchiet_languagesgenerated, author = {Graeme Ritchiet}, title = {Languages Generated by Two-Level Morphological Rules-}, year = {} }

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Abstract

The two-level model.of morphology and phonology arose from work on finite-state machine de-scriptions of phonological phenomena. However, the two-level rule notation can be given a precise declarative semantics in terms of the segmentation of sequences of pairs of symbols, quite inde-pendently of any computational representation as sets of finite-state transducers. Thus defined, the two-level model can be shown to be less powerful, in terms of weak generative capacity, than parallel intersections of arbitrary finite-state transducers without empty transitions (the usual computational representation). However, if a special boundary symbol is permitted, the full family of regular languages can be generated. Two-level morphological grammars may, without loss of generality, be written in a simplified normal form. The set of two-level generated languages can be shown to be closed under intersection, but not under union or complementation. 1. Background Koskenniemi (1983a, 1983b, 1984) proposed a rule-system for describing morphological regularities in a language, depending centrally on the idea of matching two sequences of symbols--a lexical string (made up of the lexical forms of morphemes) and a surface string (the sequence of characters in the normal, inflected, form of the word).