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<Paper uid="C00-2166">
  <Title>Robust Semantic Construction</Title>
  <Section position="3" start_page="1101" end_page="1101" type="metho">
    <SectionTitle>
2 Design Principles
</SectionTitle>
    <Paragraph position="0"> To cope with tile problems mentioned, traditional SC techniques (Montague, 1973) (Pereira and Shieber, 1987) (Bos el; al., 1996) cannot be used. Instead, the fbllowing ideas were exploited. null Modularity and Underspeeification. A major problem in SC is the treatment of mnbiguity. Often the local rule context available in SC does not give enough ilffonnation to resolve such ambiguities. In these cases, underspecification should be used to defer the resolution of choices. Thus, the described module builds a lexically and scopally underspecified representation. Subsequently the lexical ambiguities are resolved by disambiguation modules.</Paragraph>
    <Paragraph position="2"> So maybe we should move into the next week</Paragraph>
    <Section position="1" start_page="1101" end_page="1101" type="sub_section">
      <SectionTitle>
Modularity and Syntax-Semantics-
</SectionTitle>
      <Paragraph position="0"> Interface. To facilitate modularity a syntax-semantics-interface is explicitly defined. The input of every parser is mapped onto an interface structure called application twe, see Figure 2. In this way input Dora various sources can be processed with a minimum of effort.</Paragraph>
      <Paragraph position="1"> Semantic Database. Great emphasis is laid on an external database of semantic predicates (Heinecke and Worm, 1996). This database associates lemmas with predicate nmnes, semantic classes and subcategorization frames (see the entry in Figure 3).</Paragraph>
    </Section>
  </Section>
  <Section position="4" start_page="1101" end_page="1101" type="metho">
    <SectionTitle>
3 System Overview
</SectionTitle>
    <Paragraph position="0"> The process of SC can be split into two phases (see Figure 4). In the first, phase an application I;ree is traversed and simultaneously an under-specified semantic representt~tion is lmilt (compositional semantic construction, see section 5).</Paragraph>
    <Paragraph position="1"> In the second phase the semantic representation is partially (lisambiguated (see section 6). The two phases are preceded by a step which me.diates between the actual output of the syntax and the syntax-semantics-interface.</Paragraph>
  </Section>
  <Section position="5" start_page="1101" end_page="1103" type="metho">
    <SectionTitle>
4 Syntax-Semantics-Interface
</SectionTitle>
    <Paragraph position="0"> Traditionally, the content of the syntax-semantics-interface is somewhat contentious.</Paragraph>
    <Paragraph position="1"> While syntax-oriented approaches try to integrate a good part of SC already into the parsing process (cf. the construction of f-structure in LFG), other al)proaches put tile main focus on semantics (e.g. Montague Grammar). To achieve a high degree of flexibility, a modular SC system has to settle for the lowest, common denonfinator of all input sources. The following information seems to be minimally required from the syntax.</Paragraph>
    <Paragraph position="2">  (l) The parser should d(~livcr a tree tbr the parsed string whi(:h the SC system then ('an convert into a hierarchical stmmian'e of senmnti(: o\])(;rations (an applicatiml, tree).</Paragraph>
    <Paragraph position="3"> (2) Every word in the input string should 1)e syntactically classified, i.e. assigned a .~!lntactic cateflo'r!/ or \])art of Sl)(;e.(:h tag. \Y=e will as-Sllllle that the parser assigns every word exactly one category. (Lexical underslmcification could conceivatfy b(; used to deal with multiple categories.) Then morphological analysis (either in synt;ax or SC) maps l;he word cate~rory pair to a morphological lemma and a set of morphologie::fl features. SC records the feal;llres in the VIT while it uses l;he lemma as a key to the semantic lexicon. In (:ase the lemma is unknown in the semantic lexicon, the, syst, eln uses the syn~ tacti(: category to automati(:ally asso(:iate ~ new  each of the categories on its right-hand side exactly one grammatical role (GR). It7 the grmmnar does not do this, ORs must be deternfined in the prel)roeessing step (e.g. determiners in NPs are specifiers). Gll.s are llsed to COlttro\]. the choice of s,.;nmntic el)orations. The set of CHs emlfloyed is; inspired by HPSG (Pollard and Sag, 1994:):</Paragraph>
    <Paragraph position="5"/>
    <Section position="1" start_page="1102" end_page="1103" type="sub_section">
      <SectionTitle>
5.1 Senmntic Construction on the
ConsGtuent Structure
</SectionTitle>
      <Paragraph position="0"> Figure 5 shows two adjun(:tion operations: In the firs/: one, the inl:erseetive a(kiunct into the next week is adjoined to move. In the second one, maybe is adjoined to the clause. The picture makes clem' what the data structure for a partial result should look like: a set of constraints and some pointers to variables in these constraints (e.g. the partial result for maybe would be { maybe(l~,lq),12 &lt; hl,ll C- la }~ and (12, la)). Since only finitely many pointers J ln a VIT, every predicate is referenced over a base label (e.g. lj for maybe). The constraint 12 &lt; ha says that; the box 12 is subordinated to box lq, while l: C la sl;a|;es t, hat; predicate l: is in box la.</Paragraph>
      <Paragraph position="1">  are involved, they can be collected in a record.</Paragraph>
      <Paragraph position="2"> All partial results are classified into six semantic types according to the pointers they allow for: nhead (nominal head, ibr nouns), vhead (verbal head, for verbs), adj (adjuncts ~, for adverbs, adjectives, subclanses, PPs, also prepositions and subordinating co~\junctions), ncomp (nonfinal complements, for pronouns, NPs, also determiners), vcomp (verbal complements, for sentences and complement clauses, also sentence moods and complementizers), cnj (tbr coordinating conjunctions).</Paragraph>
      <Paragraph position="3"> Semantic operations expect arguments of specific semantic types: Complementation combines heads with complements, Adjunction combines heads with adjuncts. Specification converts an incoml)lete ncomp (i.e. a deternfiner) and a nhead into a complete ncomp. Coordination combines a cnj with a series of partial results of equal type.</Paragraph>
      <Paragraph position="4"> If a type clash occurs, a &amp;quot;type raising&amp;quot; operation is invoked. Such operations usually insert specific abstract predicates that represent phonetically empty words or elided materiM still to be retrieved by ellipsis resolution in a later step. Figure 6 gives a concise description of these operations a. Consider some type-raising exmnples:  (2) I will come if necessary.</Paragraph>
      <Paragraph position="5"> star (adj --+ vhead) (3) Afternoon might work or early morniT~,g.</Paragraph>
      <Paragraph position="6"> abstr_ tel (ncomp -+ vhead)</Paragraph>
    </Section>
    <Section position="2" start_page="1103" end_page="1103" type="sub_section">
      <SectionTitle>
5.2 Semantic Construction on the
Predicate-Argument Structure
</SectionTitle>
      <Paragraph position="0"> While the application tree (Figure 2) states that the pronoun we is the subject of should, in the 2VITs provide a lexical underspecification class for intersective (e.g. into the vext week and scopal adjuncts (e.g. maybe). Thus, SC has to handle intersecLive and seopal adjunction in parallel.</Paragraph>
      <Paragraph position="1"> 3In Figure 6 the following names are used for newly inserted predicates: udef (mill determiner), unspcc_ rood (mill preposition), stat (auxiliary verb be), abstr_nom (nominal ellipsis), abstr_ tel (verbal ellipsis), dccl (declarative sentence mood), poss (relation expressed by ge.nitive), de.f (definite quantifier).</Paragraph>
      <Paragraph position="3"> semantic representation (Figure 1) we is the sub-ject of move. So in this case head and semantic subject m:e not in the same local rule. To retrace such non-local dependencies, a slash device is used to store the pertinent information (the argument variable and the box label of the head) and propagate it through the application tree in search for a licenser. If a subcategorized element occurs without a subcategorizing head (as occurs often in fl'agmentary input), an elliptical element is assumed:  (4) I mean if you --~ absh'_ 'tel with subject you</Paragraph>
    </Section>
  </Section>
  <Section position="6" start_page="1103" end_page="1104" type="metho">
    <SectionTitle>
6 Noncompositional Semantic
Construction
</SectionTitle>
    <Paragraph position="0"> In noncompositional SC idioms are recognized m~d a higher level of abstraction is achieved.</Paragraph>
    <Paragraph position="1"> Technically, noncompositional SC is about transforming VITs. Thus, for implementation the VIT transfer package of Dorna and Emele ((1996)) is used. Linguistically, the component performs the following tasks: * recognition of multi-word lexemes that arc not designated as such by syntax (e.g. greeting expressions good night, comparatives more comfortable) * recognition and comput~tion of clock times (e.g. a qm~rter to ten) and (late expressions * recognition of titles (e.g. Frau Miiller) * partial dismnbiguation of sentence mood (e.g. who did it; is recognized as a question) * distribution of conjoined material, if required by the level of abstraction aimed for  (e.g. clock tilnes between a. quarter to and half l)aSt to, n, (late expressions Monday the</Paragraph>
  </Section>
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