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<Paper uid="C96-2109">
  <Title>An Evaluation Semantics for DATR Theories</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> DATR was originally introduced by Evans and Gazdar (1989a; 1989b) as a simple, non-monotonic language for representing lexical inheritance hierarchies. A DATR hierarchy is defined by means of path-value specifications. Inheritance of values permits appropriate generalizations to be captured and redundancy in the description of data to be avoided. A simple default mechanism provides for concise descriptions while allowing for particular exceptions to inherited information to be stated in a natural way.</Paragraph>
    <Paragraph position="1"> Currently, DATR is the most widely-used lexical knowledge representation language in the natural language processing community. The formalism has been applied to a wide variety of problems, including inflectional and derivational morphology (Gazdar, 1992; Kilbury, 1992; Corbett and Fraser, 1993), lexical semantics (Kilgariff, 1993), morphonology (Cahill, 1993), prosody (Gibbon and Bleiching, 1991) and speech (Andry et al., 1992). In more recent work, DATR has been used to provide a concise, inheritance-based encoding of Lexiealized Tree Adjoining Grammar (Evans et al., 1995). There are around a dozen different implementations of DATR in existence and large-scale DATR lexicons have been designed for use in a number of natural language processing applications (Cahill and Evans, 1990; Andry et al., 1992; Cahill, 1994). A comprehensive, informal introduction to DATR and its application to the design of natural language lexicons can tbund in (Evans and Gazdar, 1996).</Paragraph>
    <Paragraph position="2"> The original publications on DATR sought to provide the language with (1) a formal theory of inference (Evans and Gazdar, 1989a) and (2) a model-theoretic semantics (Evans and Gazdar, 1989b). Unfortunately, the definitions set out in these papers are not general enough to cover all of the constructs available in the DATR language.</Paragraph>
    <Paragraph position="3"> In particular, they fail to provide a full and correct treatment of DATR's notion of 'global inheritance', or the widely-used 'evaluable path' construct. A denotational semantics for DATR that covers all of the major constructs has been presented in (Keller, 1995). However, it still remains to provide a suitably general, formal theory of inference for DATR, and it is this objective that is addressed in the present paper.</Paragraph>
  </Section>
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