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<Paper uid="W91-0112">
  <Title>A GENERAL COMPUTATIONAL METHOD FOR GRAMMAR INVERSION</Title>
  <Section position="9" start_page="96" end_page="96" type="concl">
    <SectionTitle>
CONCLUSIONS
</SectionTitle>
    <Paragraph position="0"> We described a general method for inversion of logic grammars that transforms a parser into an efficient generator using an off-line compilation process that manipulates parser's clauses. The resulting &amp;quot;inverted-parser&amp;quot; generator behaves as if it was &amp;quot;parsing&amp;quot; a structured representation translating it into a well-formed linguistic string. The augmented grammar compilation procedure presented here is already quite general: it appears to subsume both the static compilation procedure of Strzalkowski (1990c), and the head-driven grammar evaluation technique of Shieber et al. (1990).</Paragraph>
    <Paragraph position="1"> The process of grammar inversion is logically divided into two stages: (a) computing the collections of minimal sets of essential arguments (MSEAs) in predicates, and (b) rearranging the order of goals in the grammar so that at least one active MSEA is &amp;quot;in&amp;quot; in every literal when its expansion is attempted. The first stage also includes computing the &amp;quot;in&amp;quot; and &amp;quot;out&amp;quot; arguments. In the second stage, the goal inversion process is initialized by the procedure INVERSE, which recursively reorders goals on the right-hand sides of clauses to meet the MSEA-binding requirement. Deadlocked clauses which cannot be ordered with INVERSE are passed for the interclausal ordering with the procedure I/qTERCLAUSAL. Special treatment is provided for recursive goals defined with respect to properly ordered series of arguments. Whenever necessary, the direction of recursion is inverted allowing for &amp;quot;backward&amp;quot; computation of these goals. This provision eliminates an additional step of grammar normalization.</Paragraph>
    <Paragraph position="2"> In this paper we described the main principles of grammar inversion and discussed some of the central procedures, but we have mostly abstracted from implementation level considerations. A substantial part of the grammar inversion procedure has been implemented, including the computation of minimal sets of essential arguments, and is used in a Japanese-English machine translation system. 24</Paragraph>
  </Section>
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