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<Paper uid="J87-1004">
  <Title>AN EFFICIENT AUGMENTED-CONTEXT-FREE PARSING ALGORITHM 1</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> Parsing efficiency is crucial when building practical natural language systems on smaller computers such as personal workstations. This is especially the case for interactive systems such as natural language database access, interfaces to expert systems, and interactive machine translation. This paper introduces an efficient on-line parsing algorithm, and focuses on its practical application to natural language interfaces.</Paragraph>
    <Paragraph position="1"> The algorithm can be viewed as a generalized LR parsing algorithm that can handle arbitrary context-free grammars, including ambiguous grammars. Section 2 describes the algorithm by .extending the standard LR parsing algorithm with the idea of a &amp;quot;graph-structured stack&amp;quot;. Section 3 describes how to represent parse trees efficiently, so that all possible parse trees (the parse forest) take at most polynomial space as the ambiguity of a sentence grows exponentially. In section 4, several examples are given. Section 5 presents several empirical results of the algorithm's practical performance, including comparison with Earley's algorithm. In section 6, we discuss how to enhance the algorithm to handle augmented context-free grammars rather than pure context-free grammars. Section 7 describes the concept of on-line parsing, taking advantage of left-to-right operation of our parsing algorithm. The on-line parser parses a sentence strictly from left to right, and starts parsing as soon as the user types in the first word, without waiting for the end of line. Benefits of on-line parsing are then discussed. Finally, several versions of on-line parser have been implemented, and they are mentioned in section 8.</Paragraph>
  </Section>
class="xml-element"></Paper>