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<Paper uid="H93-1032">
  <Title>INDEXING AND EXPLOITING A DISCOURSE HISTORY TO GENERATE CONTEXT-SENSITIVE EXPLANATIONS</Title>
  <Section position="10" start_page="169" end_page="169" type="concl">
    <SectionTitle>
6. Related Work
</SectionTitle>
    <Paragraph position="0"> Computational linguists have investigated how the context provided by the previous discourse should affect the generation of referring expressions, including pronominalization decisions (e.g., \[14, 15\]). Others have studied how a more extensive discourse history could affect other aspects of the response. Swattout's XPLAIN system can suggest simple analogies with previous explanations and omit portions of a causal chain that have been presented in an earlier explanation. However, this is the only type of contextual effect implemented in XPLAIN, and it was done so using an ad hoc technique to provide this one effect. We are attempting to provide a more general approach.</Paragraph>
    <Paragraph position="1"> McKeown carried out a preliminary analysis of how previous discourse might affect a system's response to users' requests to describe an object or compare two objects \[16\]. She found that by simply maintaining a list of the questions that had been asked, it was possible to avoid certain types of rrepetition. She further found that if the system were to keep track of the exact information that was provided previously, it could create a text that contrasts or parallels an earlier one. While McKeown's analysis was fairly detailed, no discourse history was mainrained in the implementation, and none of the suggestions for how responses could be altered, if such a history existed, were actually implemented or tested. We are devising a way for explanation strategies to make use of the information stored in a discourse history, and axe implementing these strategies.</Paragraph>
    <Paragraph position="2"> Finally, our work bears some resemblance to work in plan adaptation \[17\]. Systems using plan adaptation often use cez techniques to index a library of previously synthesized plans.</Paragraph>
    <Paragraph position="3"> However, plan ~d,_ptation is concerned with indexing plans so that they can be retrieved and mused, perhaps with modification, in later situations. Our emphasis is not on reusing plans, hut rather on exploiting prior plans as one of many knowledge sources affecting explanation generation.</Paragraph>
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