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<Paper uid="P97-1025">
  <Title>Planning Reference Choices for Argumentative Texts</Title>
  <Section position="3" start_page="0" end_page="190" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> This paper describes how reference decisions are made in PROVERB, a system that verbalizes machine-found natural deduction (ND) proofs. A piece of argumentative text such as the proof of a mathematical theorem can be viewed as a sequence *Much of this research was carried out while the author was at Dept. of CS, Univ. of the Saarland, supported by DFG (German Research Council). This paper was written while the author was a visitor at Dept. of CS, Univ. of Toronto, using facilities supported by a grant from the Natural Sciences and Engineering Research Council of Canada.</Paragraph>
    <Paragraph position="1"> of derivations. Each such derivation is realized in PROVERB by a proof communicative act (PEA), following the viewpoint that language utterances are actions. PeAs involve referring phrases that should help a reader to unambiguously identify an object of a certain type from a pool of candidates. Concretely, such references must be made for previously derived conclusions used as premises and for the inference method used in the current step.</Paragraph>
    <Paragraph position="2"> As an example, let us look at the PeA with the name Derive below:</Paragraph>
    <Paragraph position="4"> Here, the slot Derived-Formula is filled by a new conclusion which this PeA aims to convey. It can be inferred by applying the filler of Method to the filler of Reasons as prernises. There are alternative ways of referring to both the Reasons and the Method.</Paragraph>
    <Paragraph position="5"> Depending on the discourse history, the following are two of the possible verbalizations:  1. (inference method omitted): &amp;quot;Since 1~ is the unit element of U, and u is an element of U, u * lu -- u.&amp;quot; 2. (reasons omitted): &amp;quot;According to the definition of unit element,</Paragraph>
    <Paragraph position="7"> An explicit reference to a premise or an inference method is not restricted to a nominal phrase, as opposed to many of the treatments of subsequent references found in the literature. Despite this difference, the choices to be made here have much in common with the choices of subsequent references discussed in more general frameworks (Reichman, 1985; Grosz and Sidner, 1986; Dale, 1992): they depend on the availability of the object to be referred to in the context and are sensitive to the segmentation of a context into an attentional hierarchy. Therefore, we have first to devise an architecture for natural language generation that facilitates a natural and effective segmentation of discourse. The  basic idea is to distinguish between language production activities that effect the global shift of attention, and language production activities that involve only local attentional movement. Concretely, PROVERB uses an architecture that models text generation as a combination of hierarchical planning and focus-guided navigation. Following (Grosz and Sidner, 1986) we further assume that every posting of a new task by the hierarchical planning mechanism creates new attentional spaces. Based on this segmentation, PROVERB makes reference choices according to a discourse theory adapted from Reichman (Reichman, 1985; Huang, 1990).</Paragraph>
  </Section>
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