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<Paper uid="E93-1012">
  <Title>Morphonology in the Lexicon</Title>
  <Section position="2" start_page="0" end_page="87" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> The use of inheritance mechanisms in computational linguistics has become wide-ranging, with applications in semantics, syntax, morphology and phonology. In this paper, we shall examine the applicability of such mechanisms to phonological aspects of morphology. null The inheritance-based lexical representation language, DATR, has become widely used for various aspects of linguistic description, and previous treatments of both morphological and phonological phenomena in DATR have shown its applicability to this area, both for its handling of inheritance by default, and for its ability to define hierarchical structures. For example, \[Gibbon, 1990\] describes how Kikuyu tone displacement and Arabic non-concatenative morphology can be defined in *Thanks are due to Roger Evans and Dafydd Gibbon for comments on previous drafts of this paper.</Paragraph>
    <Paragraph position="1"> DATR and \[Reinhard, 1990\] describes a hierarchical approach to German umlaut. In this paper we assume a knowledge of DATR and refer the reader to the introductions in \[Cahill and Evans, 1990\] and \[Evans and Gazdar, 1990\].</Paragraph>
    <Paragraph position="2"> MOI_USC (\[Cahill, 1990a\],\[Cahill, 1990b\],\[Cahill and Gazdar, 1990\]), is a formal language for defining 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 aspects of morphological alternations, which require reference to concepts such as &amp;quot;initial&amp;quot;, &amp;quot;final&amp;quot; and &amp;quot;penultimate&amp;quot;.</Paragraph>
    <Paragraph position="3"> An account of English verbal morphology was discussed 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 &amp;quot;mechanisms&amp;quot; needed. More importantly, however, we shall demonstrate, 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 lexicon, in which ultimately all levels of description morphology, phonology, orthography, syntax, semantics - are combined.</Paragraph>
    <Paragraph position="4">  In the following sections we shall consider the structures involved and how they may be defined in DATR, considering how to model both the precise structures used by MOLUSC and more generally useful phonological structures. We shall then consider how we might define the alternations. Finally, we shall discuss the advantages of this approach over previous descriptions of such phenomena as well as over the original MOLUSC language.</Paragraph>
  </Section>
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