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<Paper uid="P98-2199">
  <Title>Segregatory Coordination and Ellipsis in Text Generation</Title>
  <Section position="3" start_page="0" end_page="1220" type="intro">
    <SectionTitle>
2 Generation Architecture
</SectionTitle>
    <Paragraph position="0"> Traditional text generation systems contain a strategic and a tactical component. The strategic component determines what to say and the order in which to say it while the tactical component determines how to say it. Even though 1The string enclosed in symbols \[ and \] are deleted from the surface expression, but these concepts exist in the semantic representation.</Paragraph>
    <Paragraph position="1">  the strategic component must first decide which clauses potentially might be combined, it does not have access to lexical and syntactic knowledge to perform clause combining as the tactical component does. We have implemented a sentence planner, CASPER (Clause Aggregation in Sentence PlannER), as the first module in the tactical component to handle clause combining. The main tasks of the sentence planner are clause aggregation, sentence boundary determination and paraphrasing decisions based on context (Wanner and Hovy, 1996; Shaw, 1995).</Paragraph>
    <Paragraph position="2"> The output of the sentence planner is an ordered list of semantic structures each of which can be realized as a sentence. A lexical chooser, based on a lexicon and the preferences specified from the sentence planner, determines the lexical items to represent the semantic concepts in the representation. The lexicalized result is then transformed into a syntactic structure and linearized into a string using FUF/SURGE (E1hadad, 1993; Robin, 1995), a realization component based on Functional Unification Grammar (Halliday, 1994; Kay, 1984).</Paragraph>
    <Paragraph position="3"> Though every component in the architecture contributes to the generation of coordinate constructions, most of the coordination actions take place in the sentence planner and the lexical chooser. These two modules reflect the two main tasks of generating coordination conjunction: the sentence planner identifies recurring elements among the coordinated propositions, and the lexical chooser determines which recurring elements to delete. The reason for such a division is that ellipsis depends on the sequential order of the recurring elements at surface level. This information is only available after syntactic and lexical decisions have been made.</Paragraph>
    <Paragraph position="4"> For example, in &amp;quot;On Monday, John rearranged cereals in Aisle 2 and cookies in Aisle 4.&amp;quot;, the second time PP is deleted, but in &amp;quot;John rearranged cereals in Aisle 2 and cookies in Aisle 4 on Monday.&amp;quot;, the first time PP is deleted. 2 CASPER only marks the elements as recurring and let the lexical chooser make deletion decisions later. A more detailed description is provided in Section 5.</Paragraph>
    <Paragraph position="5"> 2The expanded first example is &amp;quot;On Monday, John rearranged cereals in Aisle 2 and \[on Monday\], \[John\] \[rearranged\] cookies in Aisle 4.&amp;quot; The expanded second example is &amp;quot;John rearranged cereals in Aisle 2 \[on Monday I and \[John\] \[rearranged\] cookies in Aisle 4 on Monday.&amp;quot; null</Paragraph>
  </Section>
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