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<Paper uid="P95-1012">
  <Title>Compiling HPSG type constraints into definite clause programs</Title>
  <Section position="8" start_page="89" end_page="89" type="concl">
    <SectionTitle>
5 Conclusion and Outlook
</SectionTitle>
    <Paragraph position="0"> We have presented a compiler that can encode HPSG type definitions as a definite clause program.</Paragraph>
    <Paragraph position="1"> This for the first time offers the possibility to express linguistic theories the way they are formulated by linguists in a number of already existing computational systems.</Paragraph>
    <Paragraph position="2"> The compiler finds out exactly which nodes of a structure have to be examined and which don't. In doing this off-line, we minimize the need for on-line inferences. The same is true for the control information, which is also dealt with off-line. This is not to say that the interpreter wouldn't profit by a more sophisticated selection function or tabulation techniques (see, e.g., (DSrre, 1993)). We plan to apply Earley deduction to our scheme in the near future and experiment with program transformation techniques and bottom-up interpretation.</Paragraph>
    <Paragraph position="3"> Our work addresses a similar problem as Carpenter's work on resolved feature structures (Carpenter, 1992, ch. 15). However, there are two major differences, both deriving form the fact that Carpenter uses an open world interpretation. Firstly, our approach can be extended to handle arbitrarily complex antecedents of implications (i.e., arbitrary negation), which is not possible using an open world approach. Secondly, solutions in our approach have the so-called subsumption monotonicity or persistence property. That means that any structure subsumed by a solution is also a solution (as in Prolog, for example). Quite the opposite is the case in Carpenter's approach, where solutions are not guaranteed to have more specific extensions. This is unsatisfactory at least from an HPSG point of view, since HPSG feature structures are supposed to be maximally specific.</Paragraph>
  </Section>
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