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<Paper uid="E87-1036">
  <Title>Buitding Expert Systems. Addison-Wesley Publishing</Title>
  <Section position="8" start_page="223" end_page="224" type="evalu">
    <SectionTitle>
4 COliPARISON
</SectionTitle>
    <Paragraph position="0"> The notion of unification has recently emerged as a common descriptive device in many Linguistic theories Like FUG, PATR-\[\[ and HPSG (Shieber 1986). Another popular approach has been to apply attribute grammars originally developed as a theory for formal Languages (gnuth 1968). LFG and OCG can be viewed as attribute grammar systems. The trend has been towards strictly declarative descriptions of syntactic structure.</Paragraph>
    <Paragraph position="1"> Syntactic rules are often expressed in the form of complex feature sets.</Paragraph>
    <Paragraph position="2"> Our ADP system also uses features, but differs both from the unification-based approach and attribute grammar approach. The basic difference is, of course, that there is neither unification nor correspondence to attribute grammars in our system. We use a pattern matching via binary relation tests. Through blackboard approach we have gained a flexible control.</Paragraph>
    <Paragraph position="3"> Blackboard system can conveniently take into account global knowledge of the sentence. In our model dependents become &amp;quot;hidden&amp;quot; from further processing once they have been found. A regent solely represents the constituents hanging below. This makes the parsing process simpler as the number of constituents decreases during parsing. There ere, however, some cases where some information must be raised from the dependent to the regent (e.g. from conjuncts to the conjunction), so that the regent could represent the whole constituent.</Paragraph>
  </Section>
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