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<Paper uid="C96-1085">
  <Title>Restricted Parallelism in Object-Oriented Lexical Parsing</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> There are several arguments why computational linguists feel attracted by the appeal of parallelism for natural language understanding (for a survey, cf. Hahn &amp; Adriaens (1994)): the ubiquitous requirement of enhanced efficiency of implementations, its inherent potential for fault tolerance and robustness, and a flavor of cognitive plausibility based on psycholinguistic evidences from the architecture of the human language processor. Among the drawbacks of parallel processing one recognizes the danger of greedy resource demands and communication overhead for processors running in parallel as well as the immense complexity of control flow making it hard for humans to properly design and debug parallel programs.</Paragraph>
    <Paragraph position="1"> In this paper, we will consider a framework for parallel natural language parsing which summarizes the experiences we have made during the development of a concurrent, object-oriented parser. We started out with a rather liberal conception which allowed for almost unconstrained parallelism. As our work progressed, however, we felt the growing need for restricting its scope as a continuous &amp;quot;domestication process&amp;quot;. While still keeping the benefits of parallelism, we have arrived at a point where we argue for a basically serial model patched with several parallel phases rather than a basically parallel model with few synchronization checkpoints. Primarily, this change in perspective was due to large amounts of artificial ambiguities that could be traced to &amp;quot;blind&amp;quot; parallel computations with excessive resource allocation requirements. Continuously taming the parallel activities of the parser and, furthermore, sacrificing highly esteemed theoretical principles such as the completeness of the parser, i.e., the guaranteed production of all analyses for a given input, led us to determine those critical portions of the parsing process which can reasonably be pursued in a parallel manner and thus give real benefits in terms of efficiency and effectiveness.</Paragraph>
  </Section>
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