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<Paper uid="C88-1035">
  <Title>Lexical Functional Grammar in Speech</Title>
  <Section position="3" start_page="173" end_page="173" type="metho">
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3. Lexical Functional Grammar
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    <Paragraph position="0"> LFG assumes two layers of grammatical description of sentences i.e. the constituent structure level and the functional structure level. The constituent structure level caters for the surface oriented realization of sentences (e.g. word order etc.) whereas the fuctional structure level is concerned with more abstract and supposedly universal grammatical functions like SUBJect, OBject, OBLique object and the like. Lexical functional Grammars use context-free rules (like in the example above) coupled with functional schemata. These schemata (normally) relate F-structures associated with corresponding mother and daughter nodes in a c-structure (roughly speaking). The functional schemata attached to lexical items so-called semantic forms may include grammatical or semantic features, but more important, they allow a case frame notation (in particular important with verbs). It is these case frames (or valencies) that make LFG in particular attractive for prediction purposes in speech recognition., in the implementation of the LFG system F-structures are incrementally constructed by using unification, i.e. a process that accumulates information in structures and never backtracks.</Paragraph>
    <Paragraph position="1"> This process is independent of the particular order in which these structures are constructed an important aspect in speech recognition where there is inherently no predetermined order of the operations to follow.</Paragraph>
    <Paragraph position="2"> 3.1. Example Grammar G2 The following small grammar fragment should give a rough impression of the basic features of our approach. Trivial rules are omitted. Since we work within a railway inquiry environment we take special care of locative and temporal expressions. As an example, we have a special lexical category for place and station names (N-lot) and for time intervalls like &amp;quot;day&amp;quot; and &amp;quot;week&amp;quot; ete (N-temp). A particular problem in LFG is the treatment of (oblique) objects and free adjuncts. In our context, we assume all temporal modifiers to be free adjuncts and verbs to be subeategorizable for oblique locat iv e objects only (besides the normal arguments SUB J, OBJ etc.). Our approach differs from /Bresnan 1982/ in various aspects.</Paragraph>
    <Paragraph position="3"> (Technically speaking, functional schemata of the !p7t, form ( $ ($...)) = $ pose certain problems for structure prediction (generation). So we avoid them.</Paragraph>
    <Paragraph position="5"> This is the rule for questions with a question element in front.</Paragraph>
    <Paragraph position="7"> This lexical rule is viewed in the bottom-up analysis process as predicting a subject and an oblique object to appear somewhere in the sentence.</Paragraph>
    <Paragraph position="8"> depart V (I&amp;quot;PRED)=&amp;quot;DEPART&lt;(I&amp;quot;SUBJ)(tOBLLOC)&gt;&amp;quot; ($ OBLLOC OBJ PCASE) = Goal This entry predicts a subject and an oblique object which denotes a goal (like in &amp;quot;depart ...for...&amp;quot; or &amp;quot;depart...to...&amp;quot;).</Paragraph>
    <Paragraph position="9">  where approach(&amp;quot;semantic grammars&amp;quot;) and a purely surface oriented word order approach.</Paragraph>
    <Paragraph position="11"> f 1 Loc (1&amp;quot; OULLOC OBJ PCASE)= {Goal} This rule reflects the fact that &amp;quot;where&amp;quot; may play the role of an oblique location or goal object (like in examples &amp;quot;Where does the train stop&amp;quot; and &amp;quot;Where does the train go&amp;quot; but not in &amp;quot;From where does the train arrive&amp;quot;).</Paragraph>
    <Paragraph position="12"> Coventry N-lot ($ PRED) =&amp;quot;CO ~VENTRY '' This is an example entry for a place name.</Paragraph>
    <Paragraph position="13"> day N-temp (1&amp;quot; PRED ) = &amp;quot;DAY&amp;quot; For the analysis of the sentence &amp;quot;where did the train call&amp;quot; we get the c-structure  In order lo demonstrate the hole-filling capabilities of this formalism we consider the phrase &amp;quot;call * Coventry&amp;quot; with * indicating a word that was not recognized by the acoustic-phonetic component. We would get the c-structure \[VP \[V calt \[PP-loc \[P-loc * \] \[ N-loc Coventry\]\]\]\] and the t-structure</Paragraph>
    <Paragraph position="15"> This little example shows how our LFG-approach is capable to predict certain features of constituents that might appear somewhere in the sentence.</Paragraph>
    <Paragraph position="16"> Now, another important point is that L F G subcategorizes for grammatical functions not for grammatical categories. That means we have a certain flexibility at hand in that the same grammatical function (e.g. the Location deep case) may be realized in different ways (compare for instance the example sentence in L(G2) &amp;quot;Where did the train call&amp;quot; with a WH-Adverb vs. &amp;quot;The train calls at Coventry&amp;quot; with an oblique object). As the example clearly shows, grammatical functions in LFG provide an additional intermediate level of description between a semantic feature Since there are sentences that are syntactically quite acceptable (i.e. on the constituent structure level) but devious in semantic terms LFG imposes 3 additional well-formedness conditions on Fstructures. We have to assess these conditions from the pragmatic viewpoint of a real-life application (e.g. with respect to predictive power and error tolerance) (i) Functional Uniqueness (no conflicting values for an attribute allowed) This is a useful principle since we want to exclude feature &amp;quot;clashes&amp;quot;. So we would like to exclude &amp;quot;Where did the train stops&amp;quot; (tense clash) but we would not want to undertake great an effort in order to exclude &amp;quot;Where does the train stops&amp;quot; (&amp;quot;since it is clear what is meant!&amp;quot;).</Paragraph>
    <Paragraph position="17"> (ii) Completeness (A f-structure must contain all the governable grammatical functions that its predicate governs) This is an awkward condition. First of all, given the uncertainty in speech re, cognition it is hard to decide at any rate when the analysis of several (conflicting) utterances is complete. In addition, we believe that there are never ending problems with the distinction between obligatory and optional arguments of a verb. Hence we decided that all arguments in a semantic form should be regarded as optional (Only SUBJ is obligatory). A f-structure that contains more grammatical functions (out of the list given in the predicate) is grammatical better than one with less functions in itself.</Paragraph>
    <Paragraph position="18"> (iii) Coherence ( There must be no grammatical function in a f-structure that is not governed by a predicate) This is a good principle since we want to exclude superfluous arguments.</Paragraph>
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