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<Paper uid="C88-1018">
  <Title>Unification Categorial Grammar: A Concise, Extendable Gragamar for Natural Language Processing</Title>
  <Section position="4" start_page="84" end_page="84" type="concl">
    <SectionTitle>
8. Conclusion
</SectionTitle>
    <Paragraph position="0"> An attractive feature of UCG is the manner in which different levels of representation - semantic, syntactic and phonological - are built up simultaneously, by the mfiform device of unification.</Paragraph>
    <Paragraph position="1"> There axe, of course, different organizing principles at the different levels; conjunction and implication exist at the semantic level, but not at the syntactic or phonological. Nevertheless, the composit:,onal construction of all three levels takes place in the same manner, namely by the accretion of constraints on possible representations. Although we have said nothing substantive about phonology here, it seems plausible, in the light of Bach and Wheeler 1981 and Wheeler 1981, that the methodological principles of compositiouality, monotonicity and locality can also lead to illuminating analyses in the domain of sound stnmture. null UCG is distinctive in the particular theory of semantic representation which it espouses. Two iilcidental features of InL may obscure its relation to DRT. The first is very minor: our formulas are linear, rather than consisting of &amp;quot;box-ese&amp;quot;. The second difference is that we appear to make no distinction between the set of conditions in it DRS, and the set of discourse markers. In fact, this is not the case. A simple recursive definition (similar to that for &amp;quot;free wtriable&amp;quot; in predicate logic) suffices to construct the cunmlative set of discourse markers associated with a complex condition from indices within a formula. This definition also allows us to capture the constraints on anaphora proposed by DRT. These departures from the standard DRT formalism do not adversely affect the insights of Kamp's theory, but do offer a substantial advantage in allowing a rule-by-rule construction of the representations, something which has evaded most other analyses in the literature.</Paragraph>
    <Paragraph position="2"> UCG syntax is heavily polymorphic in the sense that the category identity of a fim~tion application typically depends on the make-up of the argmnent. Thus, the result of applying a type-raised NP to a transitive verb phrase is an intransitive verb phrase, while exactly the same functor applied to an intransitive verb phrase will yield a sentence. Analogously, a prepositional moditier applied to a scntence will yield a sentence, while exactly the same functor applied to a noun will yield a noun. This approach allows us to dramatically simplify the set of categories employed by the grammar, while also retaining the fundamental insight of standard categorial grammar, namely that expressions combine as fnnctor and argument. Such a mode of combination treats head-complement relations and hcad-moditier relations as special cases, and provides an elegant typology of categories that can only be awkwardly mimicked in X-bar syntax.</Paragraph>
    <Paragraph position="3"> Finally, we note one important innovation. Standard ctttegorial grammar postulates a functor-argument pair in semantic rcpresenration which parallels the syntactic constituents; typically, lambda-abstraction is required to construct the appropriate flmctor expressions in semantics. By contrast, the introduction of signs to the right of the categorial slash means that we subsume semantic combinatioi* within a generalized fnnctional application, and the necessity ~{) consmtcting specialized flmctors in the semantics simply disaopears.</Paragraph>
  </Section>
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