Morphonology in the Lexicon

Morphonology in the Lexicon Lynne J Cahill* School of Cognitive and Computing Sciences University of Sussex, Brighton BN1 9QH, England Emaih lynneca@cogs.susx.ac.uk Abstract In this paper we present a means of defin- ing morphonological phenomena in an in- heritance based lexicon. We make use of the theory behind the formal language MOLUSC, in which morphological alterna- tions were defined as mappings between se- quences of tree-structured syllables. We discuss how the alternations can be defined in the inheritance-based lexical representa- tion language DATR, and how the phono- logical aspects can be built upon to bring it closer to an integrated lexicon with rep- resentations which can be used by both the morphology and phonology of a language. 1 Introduction The use of inheritance mechanisms in computational linguistics has become wide-ranging, with applica- tions in semantics, syntax, morphology and phonol- ogy. In this paper, we shall examine the applicability of such mechanisms to phonological aspects of mor- phology. The inheritance-based lexical representation lan- guage, DATR, has become widely used for vari- ous aspects of linguistic description, and previous treatments of both morphological and phonologi- cal phenomena in DATR have shown its applica- bility to this area, both for its handling of inher- itance by default, and for its ability to define hi- erarchical structures. For example, [Gibbon, 1990] describes how Kikuyu tone displacement and Ara- bic non-concatenative morphology can be defined in *Thanks are due to Roger Evans and Dafydd Gibbon for comments on previous drafts of this paper. DATR and [Reinhard, 1990] describes a hierarchical approach to German umlaut. In this paper we as- sume a knowledge of DATR and refer the reader to the introductions in [Cahill and Evans, 1990] and [Evans and Gazdar, 1990]. MOI_USC ([Cahill, 1990a],[Cahill, 1990b],[Cahill and Gazdar, 1990]), is a formal language for defin- ing morphological alternations as mappings between sequences of tree-structured syllables. It is based on the theory that (many) morphological alternations are phonologically based, and can best be described as operating on hierarchical structures, such as the syllable. However, there are fundamentally linear as- pects of morphological alternations, which require reference to concepts such as "initial", "final" and "penultimate". An account of English verbal morphology was dis- cussed in [Cahill, 1990b] which was expressed in a combined DATR/MOI_USC lexicon fragment. The morphological distribution was defined by the DATR while the morphological realisation was defined by a set of MOIUSC functions. In this paper, we discuss an account derived from this (see appendix), which expresses the distribution of alternations involved in the same underlying way, but which does not require a separate language to define them. In doing this, we can reduce the two-tiered DATR/MOLUSC approach originally used, to a single-tiered account. This has the obvious advantage of reducing the "mechanisms" needed. More importantly, however, we shall demon- strate, with discussion of how the morphonological information may be generalised to be more useful to the phonology proper, it also has the advantage of moving the account towards a fully-integrated lex- icon, in which …

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