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<Paper uid="E99-1002">
  <Title>Generating referring expressions with a unification grammar</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
METHOD ~I
REST I
</SectionTitle>
    <Paragraph position="0"> on the idea of a 'feedback text', i.e. a text, generated by the system, that presents the current content of the knowledge base (however incomplete) along with the set of permitted operations for extending or otherwise editing the knowledge; these operations are provided through pop-up menus which open on spans of the feedback text. Two requirements of WYSIWYM editing are that feedback texts should be generated fast (even a delay of a few seconds is irritating), and that they should express coreference relations clearly through appropriate referring expressions; reconciling these two requirements has motivated the work described here.</Paragraph>
    <Paragraph position="1"> The semantic network in figure 1 shows a knowledge base that might be produced using the ICONOCLAST 1 system, which generates patient information leaflets. At present this knowledge base defines only the goal and first step of a procedure; before generating a useful output text the author would have to add further steps. To facilitate the author's task, the program generates the following feedback text, including the 'anchor' Further steps which provides options for extending the procedure. null IICONOCLAST is supported by the Engineering and Physical Sciences Research Council (EPSRC) Grant L77102.</Paragraph>
    <Paragraph position="2"> Proceedings of EACL '99 To put on a patch: 1. Remove the patch from the box.</Paragraph>
    <Paragraph position="3"> Further steps.</Paragraph>
    <Paragraph position="4"> The program can also produce an 'output text' in which optional unspecified material is omitted. Whereas the feedback text is viewed only by the author during editing, the output text constitutes the final product which will be incorporated into the patient information leaflet. At the stage depicted by figure 1, with only one step specified, an output text could be generated if desired, but owing to the incomplete content it would read strangely: Put on a patch by removing it from the box.</Paragraph>
    <Paragraph position="5"> These simple texts already illustrate several ways in which the choice of referring expression depends upon context.</Paragraph>
    <Paragraph position="6"> * To introduce a referent into the discourse, an indefinite description (e.g. 'a patch') is usually used, although a definite description may be preferred if the referent will already be familiar to the reader ('the box').</Paragraph>
    <Paragraph position="7"> * Subsequent mentions of the referent are made through a pronoun or a definite description.</Paragraph>
    <Paragraph position="8"> In this way~ the text distinguishes references to the same token from references to two tokens of the same type. If the patch removed from the box were different from the patch to be put on, the second line of the feedback text should contain another indefinite nominal (e.g. 'Remove a second patch from the box').</Paragraph>
    <Paragraph position="9"> * Roughly, a pronoun can be used instead of a definite description if there is no danger of ambiguity, and if no major structural boundary has been passed since the referent was last mentioned. We are not concerned here with the details of this issue (Hofmann, 1989; Walker et al., 1998); in the examples, we have treated the colon in the feedback text as a major structural boundary, so preferring a definite description in the feedback text and a pronoun in the output text.</Paragraph>
    <Paragraph position="10"> We concentrate here on two contextual features, focus and prior mentions. The problem of finding suitable identifying properties (Dale and Reiter, 1995; Horacek, 1997) will not be addressed here, although as will be shown our approach could incorporate this work.</Paragraph>
  </Section>
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