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<Paper uid="H91-1042">
  <Title>Statistical Agenda Parsing</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> In a Graham/Harrison/Ruzzo (GHR) parser, the chart is used to maintain a record of syntactic constituents that have been found (terms) and grammatical rules that have been partially matched (dotted rules). Parsing strategies such as GHR, CKY and other algorithms can be viewed as methodical ways of filling the chart which guarantee to explore all possible extensions of dotted rules by terms.</Paragraph>
    <Paragraph position="1"> An agenda is an alternative chart-filling algorithm with the goal of finding some term covering the entire input without necessarily filling in all of the chart. If terms can be ranked by &amp;quot;goodness&amp;quot; and the grammar can produce multiple analyses of a given string, then one goal for an agenda is to produce the &amp;quot;best&amp;quot; parse first.</Paragraph>
    <Paragraph position="2"> The alternative goal we have chosen for DELPHI is to use the agenda mechanism to reduce the search necessary to produce ACCEPTABLE (see below) parses. This results in sparsely populated charts, approaching the extreme (and probably unattainable) goal of deterministic parsing, in which the only terms and dotted rules entered into the chart are those which appear as parts of the final parse.</Paragraph>
    <Paragraph position="3"> The techniques involved in statistical agenda parsing allow &amp;quot;low probability&amp;quot; rules to be added to a grammar without significant cost in terms of either erroneous parses or increased parse time. These low probability rules greatly increase the coverage and robustness of the system by accounting for unusual or marginal constructions.</Paragraph>
  </Section>
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