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<Paper uid="J95-2002">
  <Title>An Efficient Probabilistic Context-Free Parsing Algorithm that Computes Prefix Probabilities</Title>
  <Section position="11" start_page="198" end_page="198" type="concl">
    <SectionTitle>
RLT = RLPLT
</SectionTitle>
    <Paragraph position="0"> where PLT has a nonzero entry at (X, a) iff there is a production for nonterminal X that starts with terminal a. RL is the old left-corner relation.</Paragraph>
    <Paragraph position="1"> During the prediction step we can ignore incoming states whose RHS nonterminal following the dot cannot have the current input as a left-corner, and then eliminate from the remaining predictions all those whose LHS cannot produce the current input as a left-corner. These filtering steps are very fast, as they involve only table lookup. This technique for speeding up Earley prediction is the exact converse of the &amp;quot;linking&amp;quot; method described by Pereira and Shieber (1987, chapter 6) for improving the efficiency of bottom-up parsers. There, the extended left-corner relation is used for top-down filtering the bottom-up application of grammar rules. In our case, we use linking to provide bottom-up filtering for top-down application of productions.</Paragraph>
    <Paragraph position="2"> On a test corpus this technique cut the number of generated predictions to almost one-fourth and speeded up parsing by a factor of 3.3. The corpus consisted of 1,143 sentence with an average length of 4.65 words. The top-down prediction alone generated 991,781 states and parsed at a rate of 590 milliseconds per sentence. With bottom-up filtered prediction only 262,287 states were generated, resulting in 180 milliseconds per sentence.</Paragraph>
  </Section>
class="xml-element"></Paper>