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<Paper uid="P85-1024">
  <Title>A PRAGMATIC~BASED APPROACH TO UNDERSTANDING INTERS~NTENTIAL ~LIPSI~</Title>
  <Section position="3" start_page="0" end_page="188" type="intro">
    <SectionTitle>
INTERPRETATION OF INTERS~qTENTIAL ~LLTPSIS
</SectionTitle>
    <Paragraph position="0"> As Ltlustrated by \[EX1\], intersententiel eA1ipticaA fra@ments cannot be fully understood in and of themselves. Therefore a strate8~ for interpreting suc~ fra@ments must rely on knowledge obtained frcl sources other than the fragment itself. Three possibilities exist: the syntactic ee Ta.~n fr'~ Flowers and Dyer(198~)  form ar precedlug utterances, the seaantlo representation of preceding utterances, and expectations gleaned from understanding the preceding disQourse.</Paragraph>
    <Paragraph position="1"> The first two strategies are exemplified by the work oC Carbosoll and Hayes(1983), Hendrlx, SacerdotC/, and Sloc,~( 1976), Waltz( 1978), and Velschedel and 3ondhelmer( 1982 ). Several limitations exist in these approaches, includiug an inabilit 7 to handle utterances that rely upon an assumed communication of the underlying task and difficulty in resolving ambiguity =&amp;quot;oug multiple interpretations. Consider the following two dislo~e sequences: SPEAE~R: &amp;quot;I want to take a bus.</Paragraph>
    <Paragraph position="2"> The cost?&amp;quot; SPEAKER: &amp;quot;I want to purchase a bus.</Paragraph>
    <Paragraph position="3"> The cost?&amp;quot; Zf a semantic strategy is employed, the case frame representation for &amp;quot;bus&amp;quot; may have a &amp;quot;cost of bus&amp;quot; and a &amp;quot;cost of bus ticket&amp;quot; slot; a~hlgulty arises regardlug to which slot the elliptical fr~sment &amp;quot;The cost?&amp;quot; refers. Althou~ one might suggest extensions far handling this fra~ent, a semantic strategy alone does not provide an adequate frame~wurk for Interpreting intersentential ellipsis. The third potential strategy utilizes a model c~ the information-seeker's inferred tank-related plan and discourse ~oals. The power of this approach is its reliance upon pragmatic information, including discourse content and conversetiona~ goals, rather than upon precise representations of the preceding utterances alone. Allen(1980) was the first to relate ellipsis processlug to the domain-dependent plan underlying a speaker's utterance. Allen views the speaker's utterance as part of a plan which the speaker has constructed and is executlug to accomplish his overall task-related goals. To interpret elliptical fragments, Allen first constructs a set of possible surface speech act representations for the elliptical fragment, limited by syntactic clues appearing within the fragment. The task-related ~oals which the speaker might pursue form a set o1&amp;quot; expectations, and Allen attempts to infer the speaker's ~al-related plan which resulted in execution of the observed utterance. A part of this inference process involves determining which of the partially constructed plans connecting expectations (goals) and obeerved utterance are 'reasonable given the knovled~ and mutual beliefs of the speaker and hearer. Allen selects the surface speech act which produced the most reasonable inferred plan as the correct interpretation.</Paragraph>
    <Paragraph position="4"> Allen notes that the speaker's fragment must identif7 the subg~als which the spea~er is pursu-Lug, but claims that in very restricted dmaains, identifying the speaker's overall ~ from the utterance ls sufficient to identify the appropriate response in terms of the obstacles present in such a plan. For his restricted do~aln involving train arrivals and departures, Allen's Interpretstlon strategy vurke well. In more complex domains, it Is necessary to identify the particular aspect of the speaker's overall task-related plan addressed by the clliptlcal frasment in order to interpret It properly. More recently, Litman and Allen(198q) have extended Allen's model to a hierarchy of task-plans and meta-plans. Litman is currently studying the interpretation of elliptical frasments within this enhanced framework. In addition to the syntactic, semantic, and plan-based strategies, a few other heuristics have been utilized. Carbusoll(1983) uses discourse expectation rules that suggest a set of expected user utterances and relate elliptical f~a~ents to these expected patterns. For example, if the syst~a asks the user whether a particular value should be used an the filler oPS a slot in a case frane, the system then expects the user's utterance to contain a confirmation or disson~Irmatlon pattern, a different filler for the slot, a comparative pattern such as &amp;quot;too hard&amp;quot;, and so forth. Although these rules use expectations about how the speaker m~ght respond, they seem to have llttle to do with the expected discourse goals of the speaker.</Paragraph>
    <Paragraph position="5"> Real understanding consists sot only of resognlzAr~ the particular surface-request or surface-lnform, but also of inferring what the speaker wants to accomplish and the relationship of each utterance to this task. Interpretation of ellipsis based upon the speaker's inferred under~ lying task-related plan and discourse Eoals facilitates a richer interpretation of elliptical utterances.</Paragraph>
  </Section>
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