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<Paper uid="W99-0108">
  <Title>Q @ @ @ O O O @ @ O @ O O @ @ 0 @ @ O @ O @ O O O @ @ @ O @ O O @ @ O O @ @ O @ O O O O Generating Anaphoric Expressions: Pronoun or Definite Description?</Title>
  <Section position="15" start_page="68" end_page="69" type="concl">
    <SectionTitle>
10 Conclusions
</SectionTitle>
    <Paragraph position="0"> Pronouns occur frequently in texts and have been hypothesized to play a significant role in text coherence.</Paragraph>
    <Paragraph position="1"> Yet, pronoun generation has not been studied in detail.</Paragraph>
    <Paragraph position="2"> If future natural language generation systems are to produce coherent, natural texts, they must use rules for generating pronouns that produce pronouns in roughly the same places that human-produced texts do. M~oreover, the rules must be based on informationthat would bc available to a sentence generator. At thesame time, in order to evaluate rules, they must be based on information that can be gleaned from a text.</Paragraph>
    <Paragraph position="3"> In this work we have argued that discourse structure  in terms of multiple threads provides an explanation for patterns of pronoun use in naturally occurring text. As a particular instantiation of a threaded discourse Structure, we looked at changes in setting, as indicated by changes in time. That is, even in places where a pronoun would be unambiguous, a definite description might be used when the time of the sentence is different from the time of the sentence in which the previous mention was made. This hypothesis provides an explanation for many of the uses of definite descriptions found in the studied texts. Other uses of definite descriptions occur because of ambiguities. We have suggested a rule which addresses when such ambiguities should not preclude the generation &amp;quot;of a pronoun. Our scheme appears to be a reasonable explanation for the patterns of pronoun use found in our corpus.</Paragraph>
    <Paragraph position="4"> Acknowledgments. This work was done while the first author was visiting the Institute for Research in Cognitive Science and while the second author was a postdoctoral fellow there (NSF SBR 8920230). We would fike to thank Jennifer Arnold and the centering group at UPenn for helpful discussions. We would also like to thank the anonymous reviewers.</Paragraph>
  </Section>
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