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<Paper uid="E89-1007">
  <Title>ON THE GENERATIVE POWER OF TWO.LEVEL MORPHOLOGICAL RULES</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
BACKGROUND
</SectionTitle>
    <Paragraph position="0"> Koskenniemi(1983a,b;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). In principle, symbols could be orthographic or phonological; here we shall follow common practice within two-level morphology, and assume orthographic forms are being analysed. Koskenniemi(1983a) originally described the rules in two alternative forms high-level rules and finite-state transducers, and conjectured that an automatic compilation procedure could be devised to transform the more readable, high-level form into the more directly implementable transducer form. His implementation was an interpreter for the transducers, which were directly written by the linguist as rules in their own right. The various linguistic analyses presented in Dalrymple et al.(1983) also follow this approach, expressing rules as transition tables for transducers. Koskenniemi(1985) refined the notation and sketched a compilation method, and Ritchie, Black et a1.(1987), Karttunen et al.(1987) describe compilation techniques for two variants of the notation. null The aim of this paper is to give an alternative statement of the meaning of the original high-level rule notation, without recourse to compilation into finite-state transducers. The benefits of this are twofold: (i) alternative implementation techniques can be considered or discussed with reference to a standard interpretation which is not tied to an existing approach to implementation; null (ii) the formal properties of the actual rule-formalism can be assessed, rather than the formal properties of another formalism (transducers) which might in principle be more powerful.</Paragraph>
    <Paragraph position="1"> In particular, it is possible to show that the two-level morphological mechanism is more limited than the transducer model in its ability to define relationships between strings.</Paragraph>
  </Section>
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