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<Paper uid="P84-1082">
  <Title>AUTOMATIC CONSTRUCTION OF DISCOURSE REPRESENTATION STRUCTURES</Title>
  <Section position="6" start_page="399" end_page="400" type="concl">
    <SectionTitle>
4 Discourse Representation Structures
</SectionTitle>
    <Paragraph position="0"> In this section we give a brief description of Kamp's Discourse Representation Theory (DRT). For a more detailed discussion of this theory and its general ramifications for natural language processing, cf. the papers by Kamp (1981) and Guenthner (1984a, 1984b).</Paragraph>
    <Paragraph position="1"> According to DRT, each natural language sentence (or discourse) is associated with a so-called Discourse Representation Structure (DRS) on the basis of a set of DRS forrnatior rules. These rules are sensitive to both the syntactic structure of the sentences in question as well as to the DRS context in which in the sentence occurs.</Paragraph>
    <Section position="1" start_page="399" end_page="399" type="sub_section">
      <SectionTitle>
4.1 Definition of Discourse Representation Struc-
tures
</SectionTitle>
      <Paragraph position="0"> A DRS K for a discourse has the general form K = &lt;U, Con&gt; where U is a set of &amp;quot;discourse referents&amp;quot; for K and Con a set of &amp;quot;conditions&amp;quot; on these individuals. Conditions can be either atomic or complex. An atomic condition has the form P(tl,...,tn) or tl=c, where ti is a discourse referent, c a proper name and P an n-place predicate.</Paragraph>
      <Paragraph position="1"> Of the complex conditions we will only mention &amp;quot;implicational&amp;quot; conditions, written as K1 IMP K2, where K1 and K2 are also DRSs. With a discourse D is thus associated a Discourse Representation Structure which represents D in a quantifier-free &amp;quot;clausal&amp;quot; form, and which captures the propositional import of the discourse.</Paragraph>
      <Paragraph position="2"> Among other things, DRT has important consequences for the treatment of anaphora which are due to the condition that only those discourse referents are admissible for a pronoun that are accessible from the DRS in which the pronoun occurs (A precise definition of accessibility is given in Ramp (1981)).</Paragraph>
      <Paragraph position="3"> Discourse Representation Structures have been implemented by means of the three relations AS-SERTION, ACCESSIBLE, and DR shown in the appendix. These three relations are written out to the relational database system (Astrahan &amp;al (1976)) after the current text has been processed.</Paragraph>
    </Section>
    <Section position="2" start_page="399" end_page="400" type="sub_section">
      <SectionTitle>
4.2 From Intermediate Structures to DRSs
</SectionTitle>
      <Paragraph position="0"> The Intermediate Structures are processed starting at the top. The transformation of all the items in the Intermediate Structure are relatively straightforward, except for the proper semantic representation of pronouns. According to the spirit of DRT, pronouns are assigned discourse referents accessible from the DRS in which the pronoun occurs. In the example given in the appendix, as we can see from the ACCESSIBLE table there are only two discourse referents available, namely ul and u2.</Paragraph>
      <Paragraph position="1"> Given the morphological information about these individuals the pronoun &amp;quot;it&amp;quot; can only be assigned the discourse referent u2 and this is as it should be.</Paragraph>
      <Paragraph position="2"> For further problems arising in anaphora resolution in general cf. Kamp (1981) and Guenthner and Lehmann (1983).</Paragraph>
      <Paragraph position="3"> 5 Remarks on work in progress We are at present engaged in extending the above construction algorithm to a much wider variety of linguistic structures, in particular to the entire fragment of English covered by the USL grammar.</Paragraph>
      <Paragraph position="4"> Besides incorporating quite a few more aspects of discourse structure (presupposition, ambiguitity, cohesion) we are particularly interested in formulating a deductive account for the retrieval of information from DRSs. This account will mainly consist in combining techniques from the theory of relational database query as well as from present techniques in theorem proving.</Paragraph>
      <Paragraph position="5">  In our opinion Ramp's theory of Discourse Representation Structures is at the moment the most promising vehicle for an adequate and efficient implementation of a natural language processing system. It incorporates an extremely versatile discourse-oriented representation language and it allows the precise specification of a number of up to now intractable discourse phenomena.</Paragraph>
    </Section>
  </Section>
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