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<Paper uid="P03-2036">
  <Title>Comparison between CFG filtering techniques for LTAG and HPSG</Title>
  <Section position="4" start_page="0" end_page="0" type="metho">
    <SectionTitle>
4 Conclusion and future direction
</SectionTitle>
    <Paragraph position="0"> We presented an empirical comparison of LTAG and HPSG parsers with CFG filtering. We compared the parsers with strongly equivalent grammars obtained by converting LTAGs extracted from the Penn Tree-bank into HPSG-style. Experimental results showed that the existing CF approximation of HPSG (Torisawa et al., 2000) produced a more effective filter than that of LTAG (Poller and Becker, 1998). By investigating the different ways of CF approximation, we concluded that the global constraints in a given grammar is essential to obtain an effective filter.</Paragraph>
    <Paragraph position="1"> We are going to integrate the advantage of the CF approximation of HPSG into that of LTAG in order to establish another CFG filtering for LTAG. We will also conduct experiments on trade-offs between the degree of CF approximation and the size of approximated CFGs as in Maxwell III and Kaplan (1993).</Paragraph>
  </Section>
  <Section position="5" start_page="0" end_page="0" type="metho">
    <SectionTitle>
Acknowledgment
</SectionTitle>
    <Paragraph position="0"> We thank Yousuke Sakao for his help in profiling TNT parser and anonymous reviewers for their helpful comments. This work was partially supported by</Paragraph>
  </Section>
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