The University of Edinburgh -
Division of Informatics
Forrest Hill & 80 South Bridge

Research Paper #496

Title:Languages Generated by Two-Level Morphological Rules
Date:Apr 1991
Presented:To appear in "Computational Linguistics"
Abstract:The two-level model of morphology and phonolgy arose from work on finite-state machine descriptions 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 independently 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.

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