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<Paper uid="W97-1301">
  <Title>Resolving Bridging References in Unrestricted Text</Title>
  <Section position="3" start_page="0" end_page="0" type="relat">
    <SectionTitle>
1 Previous Work
</SectionTitle>
    <Paragraph position="0"> We are in the process of developing a system for interpreting definite descriptions (DDs) in written text without restrictions of domain. The implementation work has been supported by an analysis of definite description use in corpora of written language (Poesio and Vieira, 1997). In one of our experiments, we asked 2 subjects to classify the uses of definite descriptions in a corpus of English texts 1 using a taxonomy derived from the proposals of (Clark, 1977; Hawkins, 1978; Prince, 1981; Fraurud, 1990; Prince, 1992). In the taxonomy used in that study, we defined bridging references as those uses of definite descriptions based on previous discourse which require some reasoning in the identification of their textual antecedent (rather than just matching identical nouns). These definite descriptions may be co-referential with an entity already introduced in the discourse, but be characterized by a different head noun (as in a car.., the vehicle); or may be simply semantically related to it (in the sense that the door is related to house). Of the 1040 DDs in that corpus, 204 (20%) were identified as bridging descriptions, 312 (30%) as anaphoric (DDs and antecedents 1A set of randomly selected parsed articles fl'om the Wall Street Journal contained in the ACL/DCI CD-ROM.</Paragraph>
    <Paragraph position="1"> which co-refer and have the same head noun), and 492 (47%) as larger situation/unfamiliar (Hawkins, 1978) (Prince's discourse new (Prince, 1992)); the remaining definite descriptions were classified as idiomatic or doubtful cases.</Paragraph>
    <Paragraph position="2"> These results led us to concentrate initially on resolving same-head anaphoric DDs and on recognising larger situation/unfamiliar uses. Our analysis of the corpus suggested that many of the latter could be recognised using syntactic heuristics: e.g., on the basis of the presence of restrictive pre- and postmodification, of the presence of special predicates (such as the superlatives first, best), or because the DD occurred in a copula or appositive construction.</Paragraph>
    <Paragraph position="3"> A first prototype with these capabilities (Vieira and Poesio, 1997) achieved an overall recall of 56% and precision of 84% when tested on our corpus. Of all anaphoric DDs 72% were resolved, and 74% of all larger situation and unfamiliar uses were identified.</Paragraph>
    <Paragraph position="4"> The definite descriptions not handled by this first prototype were typically larger situation uses based on common knowledge (such as the government) and bridging descriptions. In this paper we present our subsequent work devoted to handling some of these remaining cases.</Paragraph>
  </Section>
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