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<Paper uid="W97-1311">
  <Title>Event Coreference for Information Extraction</Title>
  <Section position="8" start_page="79" end_page="80" type="concl">
    <SectionTitle>
7 Conclusion
</SectionTitle>
    <Paragraph position="0"> Event coreference is more complex than object coreference because of the requirement that objects filling particular event roles in two possibly coreferential events must themselves be coreferential. Coreferring events is therefore logically secondary to coreferring objects 4.</Paragraph>
    <Paragraph position="1"> The approach we describe here provides a very general and powerful mechanism for performing event coreference and for constructing complex event representations, such as those required for information extraction tasks. Within information extraction the problem has typically been addressed by attempting to merge, or unify, extracted templates (e.g. Sown (1984) or Appelt et al. (1995)), but a more generally useful 4Of course in some events, roles may be filled by other events, but this complication does not affect the basic point that object coreference is primary and event coreference dependent upon it.</Paragraph>
    <Paragraph position="2">  mechanism will operate within a more general representation. Our approach can be compared to that of Whittemore and Macpherson (1991) who discuss incremental building of event representations within a modified form of DRT (Kamp, 1981). However, the representation used here is preferred because it allows a tighter coupling between world or conceptual modelling and discourse modelling.</Paragraph>
    <Paragraph position="3"> The representation and the coreference mechanism are fully implemented within the LaSIE information extraction system and are currently being extended to make use of a richer model of event times, the importance of which is demonstrated in Crowe (1996). The mechanism described here is used in the LaSIE system for both object and event coreference, treating the different types simply as instances subject to differing constraints, where constraints can be easily represented at any level of generality. Our evaluation, while far from exhaustive, shows that addressing event coreference can clearly result in real benefits for IE systems.</Paragraph>
  </Section>
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