<?xml version="1.0" standalone="yes"?>
<Paper uid="W98-1206">
  <Title>The effect of alternative tree representations on tree bank grammars</Title>
  <Section position="9" start_page="493" end_page="493" type="concl">
    <SectionTitle>
7 Conclusion
</SectionTitle>
    <Paragraph position="0"> There may be several ways of representing a particular linguistic construction as a tree. Because of the independence assumptions implicit in a PCFG, the kind of tree representation employed can have a dramatic impact on the quality of the PCFG model induced. This paper introduces a new methodology for examining these effects utilitizing tree transformations, and showed that one transformation, which copies the label of a parent node onto the labels of its children, can dramatically improve the performance of a PCFG model in terms of labelled precision and recall. It also pointed out that if only maximum likelihood parses are of-interest then many productions can be ignored, since they are subsumed by combinations of other productions in the grammar.</Paragraph>
  </Section>
class="xml-element"></Paper>