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<Paper uid="P90-1020">
  <Title>TYPES IN FUNCTIONAL UNIFICATION GRAMMARS</Title>
  <Section position="7" start_page="158" end_page="158" type="concl">
    <SectionTitle>
5 CONCLUSION
</SectionTitle>
    <Paragraph position="0"> Functional Descriptions are built from two components: a set C of primitives and a set L of labels.</Paragraph>
    <Paragraph position="1"> Traditionally, all structuring of FDs is done using strings of labels. We have shown in this paper that there is much to be gained by delegating some of the structuring to a set of primitives. The set C is no longer a fiat set of symbols, but is viewed as a richly structured world. The idea of typed-unification is not new (Ait-Kaci, 1984), but we have integrated it for the first time in the context of FUGs and have shown its linguistic relevance. We have also introduced the FSET construct, not previously used in unification, endowing FUGs with the capacity to represent and reason about complete information in certain situations. null The structure of C can be used as a metadescription of the grammar: the type declarations specify what the grammar knows, and are used to check input FDs. It allows the writing of much more concise grammars, which perform more efficiently. It is a great resource for documenting the grammar.</Paragraph>
    <Paragraph position="2"> The extended formalism described in this paper is implemented in Common Lisp using the Union-Find algorithm (Elhadad, 1988), as suggested in (Huet, 1976, Ait-Kaci, 1984, Escalada-Imaz &amp; Ghallab, 1988) and is used in several research projects (Smadja &amp; McKeown, 1990, Elhadad et al, 1989, McKeown &amp; Elhadad, 1990, McKeown et al, 1991). The source code for the unifier is available to other researchers. Please contact the author for further details.</Paragraph>
    <Paragraph position="3"> We are investigating other extensions to the FU formalism, and particularly, ways to modify control over grammars: we have developed indexing schemes for more efficient search through the grammar and have extended the formalism to allow the expression of complex constraints (set union and intersection).</Paragraph>
    <Paragraph position="4"> We are now exploring ways to integrate these later extensions more tightly to the FUG formalism.</Paragraph>
  </Section>
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