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<Paper uid="P90-1026">
  <Title>Asymmetry in Parsing and Generating with Unification Grammars: Case Studies From ELU</Title>
  <Section position="9" start_page="209" end_page="209" type="concl">
    <SectionTitle>
5. Conclusion
</SectionTitle>
    <Paragraph position="0"> We have seen, in the preceding section, how in order to write grammars suitable for use with the generator, one must either modify the technical aspects of the grammar or dispense with cemfin classes of grammatical analysis (losing the benefits of relational abstraction on one hand, and lexicalism on the other, for example). Both of these may be interpreted as restricting the freedom of the grammar writer. The problematic case illustrated in section 4.2 raises the issue of non-deterrolni~m, a potential pitfall for all unification-based systems.</Paragraph>
    <Paragraph position="1"> In parsing, the result may be long processing limes, but when generating with algorithms of this class, the consequence is often non-tern~inafion. As Shieber et al. (1989, fn.4) observe, failure to choose the right daughter as the starting point for recursive generation may prevent tenuinafion.</Paragraph>
    <Paragraph position="2"> The desire to exploit the power of unification by using the lexicon as a repository of essentially syntactic (beyond pure semantic) information is natural, and has been encouraged by the success in theoretical linguistics of grammatical formalisms which employ such techniques. Yet the use of these techniques in grammar writing, which are highly attractive from the point of view of economy and expressive power, deprives the generator of information that is, strictly speaking, syntactic.</Paragraph>
    <Paragraph position="3"> Semantic heads alone are not sufficient to drive the generation process, if syntactic information cannot also be made available. Our interim conclusion is that strong versions of the lexicalist position do not appear to be compatible with our current generator, at least for a number of cases. This is not to say that it should be abandoned - the benefits in terms of clarity and economy are probably too great - but some care is needed if it is to be exploited effec- 210 lively.</Paragraph>
    <Paragraph position="4"> Given that work on this type of generation is in its early stages, it is to be hoped that confimfing research will enable less restricted grammars to be written. Nevertheless, the currently available facilities have been employed successfully in general, mJking it possible to envisage defining the 'adequacy' of a grammar in terms of its behavior both in parsing and in generation.</Paragraph>
  </Section>
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