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<Paper uid="P88-1031">
  <Title>Graph-structured Stack and Natural Language Parsing</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1. Introduction
</SectionTitle>
    <Paragraph position="0"> A stack plays an important role in natural language parsing. It is the stack which gives a parser context-free (rather than regular) power by permitting recursions. Most parsing systems make explicit use of the stack. Augmented Transition Network (ATN) \[10\] employs a stack for keeping track of retum addresses when it visits a sub-network. Shift-reduce parsing uses a stack as a pdmary device; sentences are parsed only by pushing an element onto the stack or by reducing the stack in accordance with grammatical rules. Implementation of pdnciple-based parsing \[9, 1, 4\] and categodal grammar \[2\] also often requires a stack for stodng partial parses already builL Those parsing systems usually introduce backtracking or pseudo parallelism to handle nondeterminism, taking exponential time in the worst case.</Paragraph>
    <Paragraph position="1"> This paper describes a general device, a graph-structured stack. The graph-structured stack was originally introduced in Tomita's generalized LR parsing algorithm \[7, 8\]. This paper applies the graph-structured stack to various other parsing methods. Using the graph-structured stack, a system is guaranteed not to replicate the same work and can run in polynomial time. This is true for all of the parsing systems mentioned above; ATN, shift-reduce parsing, principle-based parsing, and perhaps any other parsing systems which employ a stack.</Paragraph>
    <Paragraph position="2"> The next section describes the graph-structure stack itself. Sections 3, 4, 5 and 6 then describe the use of the graph-structured stack in shift-reduce LR parsing, ATN, Categorlal Grammars, and principle-based parsing, respectively. Section 7 discusses the relationship between the graph-structured stack and chart \[5\], demonstrating that chart parsing may be viewed as a special case of shift-reduce parsing with a graph-structured stack.</Paragraph>
  </Section>
class="xml-element"></Paper>