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<Paper uid="J99-1001">
  <Title>A Process Model for Recognizing Communicative Acts and Modeling Negotiation Subdialogues</Title>
  <Section position="4" start_page="3" end_page="7" type="intro">
    <SectionTitle>
4 We are using &amp;quot;express doubt&amp;quot; in the sense of challenging the truth of a proposition.
</SectionTitle>
    <Paragraph position="0"> Carberry and Lambert Modeling Negotiation Subdialogues (7) EA: What is Dr. Smith teaching? (8) CA: Dr. Smith is teaching Architecture.</Paragraph>
    <Paragraph position="1"> (9) EA: Isn't Dr. Brown teaching Architecture?  Figure 1 A dialogue with an expression of doubt. since otherwise the hearer could not be expected to believe that the speaker was using a conflict between Pi and Pdoubt to question the validity of Paoubt. Similarly, it must be plausible that the speaker believes that if Pi is true, then Pdoubt is not; otherwise the hearer could not be expected to think that the speaker believes that the truth of Pi raises doubts about Pdoubt.</Paragraph>
    <Paragraph position="2"> Although being able to ascribe beliefs as plausible is necessary for recognition of all discourse actions, some discourse actions, such as the expressions of doubt that we consider in this paper, require further evidence. This evidence is provided by linguistic, world, and contextual knowledge. These knowledge sources can either provide evidence for a generic discourse act (such as an expression of doubt) or evidence that the conditions are satisfied for performing a specific discourse act (such as expressing doubt that Dr. Smith is teaching Architecture). In addition, contextual knowledge can suggest a particular interpretation when equivalent evidence exists for several specific discourse acts. These knowledge sources are discussed in the next sections.</Paragraph>
    <Section position="1" start_page="4" end_page="4" type="sub_section">
      <SectionTitle>
3.1 Linguistic Knowledge
</SectionTitle>
      <Paragraph position="0"> 3.1.1 Evidence for a Generic Discourse Act. A number of researchers (Reichman 1978, 1985; Grosz and Sidner 1986; Polanyi 1986; Cohen 1987; Hirschberg and Litman 1987; Litman and Allen 1987; Schiffrin 1987; Hinkelman 1989; Litman and Hirschberg 1990; Knott and Dale 1994; Knott and Mellish 1996; Marcu 1997) have investigated the use in discourse of special words and phrases such as but, anyway, and by the way.</Paragraph>
      <Paragraph position="1"> They found that these clue words, or discourse markers, have a number of different functions, including indicating the role of an utterance in the dialogue, conveying the relationship between utterances, suggesting shifts in focus of attention, conveying the structure of the discourse, etc.</Paragraph>
      <Paragraph position="2"> Consider again the dialogue shown in Figure 1. If EA had followed (7)-(8) with (9a) (9)a. EA: Isn't Architecture one of our required courses? then EA's utterance would not be interpreted as expressing doubt but would instead be understood as merely seeking information about the Architecture course. However, if this utterance is preceded by the clue word but, as in (9b) below, (9)b. EA: But isn't Architecture one of our required courses? then the utterance is expressing doubt, though we have difficulty ascertaining the reason for this doubt--perhaps EA believes that Dr. Smith does not teach courses that students are required to take! Thus, clue words comprise one source of evidence in the recognition of discourse acts. In particular, a clue word can provide evidence for a generic discourse act, such as Express-Doubt, but it remains for other sources to resolve what is being doubted. Computational Linguistics Volume 25, Number 1 3.1.2 Evidence for a Specific Discourse Act. Expressions of doubt do not always include clue words, as illustrated by utterance (9) in Figure 1. In the absence of a clue word, we need evidence that the speaker holds the three beliefs, listed earlier in Section 3, for performing a specific discourse act. Evidence for the second belief (that the speaker believes that Pi is true) is often provided by the surface form of the utterance, such as an utterance of the form &amp;quot;Isn't Pi ?&amp;quot;--for example, &amp;quot;Isn't Dr. Brown teaching Architecture?&amp;quot; in (9). This surface form indicates a strong belief in the queried proposition while a simple yes-no question, such as &amp;quot;Is Dr. Brown teaching Architecture?&amp;quot;, does not. Therefore, if EA were to follow (7)-(8) with &amp;quot;Is Dr. Brown teaching Architecture?&amp;quot;, EA would seem to have a misconception that more than one person can teach a course or perhaps be seeking information in order to subsequently express doubt--but the utterance itself is not conveying doubt that Dr. Smith is teaching Architecture. Thus the surface form of the utterance is one source of evidence that the speaker holds the requisite beliefs for performing a specific discourse act.</Paragraph>
    </Section>
    <Section position="2" start_page="4" end_page="4" type="sub_section">
      <SectionTitle>
3.2 World Knowledge
</SectionTitle>
      <Paragraph position="0"> World knowledge in the form of stereotypical beliefs is another source of evidence that the speaker holds the requisite beliefs for a particular discourse act. For example, world knowledge can provide evidence for the third speaker belief, that if Pi is true, then Pdoubt is not. Suppose that it is stereotypically believed that prestigious fellowships are awarded for sabbaticals, that faculty on sabbatical do not teach, and that faculty only teach in their area of expertise. Consider the dialogue shown in Figure 2.</Paragraph>
      <Paragraph position="1"> After (13), there are two propositions that have been conveyed by CA but not yet completely accepted by EA: the proposition that Dr. Smith is not on sabbatical and the proposition that Dr. Smith is teaching CS360, cormnunicated by utterances (13) and (11), respectively. A subsequent utterance might express doubt at one of these propositions or might forego the opportunity to doubt them, perhaps by pursuing some discourse act unrelated to either of the propositions. Consider the following three possible continuations of the dialogue: (14)a.</Paragraph>
      <Paragraph position="2">  b.</Paragraph>
      <Paragraph position="3"> C.</Paragraph>
      <Paragraph position="4"> EA: Wasn't Dr. Smith awarded a Fulbright? EA: Isn't Dr. Smith a theory person? EA: Isn't Dr. Smith an excellent teacher?  While (14a) and (14b) seem to be expressing doubt, (14c) is simply seeking further information about Dr. Smith. The reason for this difference in interpretation is that in the case of (14a) and (14b), evidence from world knowledge suggests that EA believes that Pi (the proposition that EA contends is true) implies that one of the two open propositions is false, whereas no such evidence exists in the case of (14c). In the case of (14a), since it is stereotypically believed that prestigious fellowships are awarded for sabbaticals, EA's utterance should be interpreted as expressing doubt at the proposition that Dr. Smith is not on sabbatical. In the case of (14b), since Dr. Smith being a theory person is an alternative to Dr. Smith being a systems person and it is stereotypically believed that being a systems person is necessary for teaching CS360 (a systems course), EA's utterance would instead be interpreted as expressing doubt at the proposition that Dr. Smith is teaching CS360. Thus, world knowledge in the form of stereotypical beliefs is another source of evidence that the speaker holds the requisite beliefs for performing a particular discourse act.</Paragraph>
      <Paragraph position="5"> If EA had uttered (14c), EA's utterance would be interpreted as merely seeking  new information since there is no domain knowledge suggesting that EA believes that Dr. Smith being an excellent teacher contributes to determining whether Dr. Smith is Carberry and Lambert Modeling Negotiation Subdialogues (10) EA: Who is teachir~g CS360 (a systems course)? (11) CA: Dr. Smith is teaching CS360.</Paragraph>
      <Paragraph position="6"> (12) EA: Isn't Dr. Smith on sabbatical? (13) CA: No, Dr. Smith is not on sabbatical.</Paragraph>
      <Paragraph position="7">  A dialogue with two open propositions.</Paragraph>
      <Paragraph position="8"> on sabbatical or to identifying the instructor of CS360. Note that (14c) demonstrates why plausibility alone is insufficient for recognition. Although there is no evidence that EA believes that Dr. Smith being an excellent teacher implies that Dr. Smith is on sabbatical or that Dr. Smith is not teaching CS360, there is also no evidence to the contrary, and thus it is plausible that EA believes that Dr. Smith being an excellent teacher indicates that he is on sabbatical or that he is not teaching CS360. This is not sufficient, however, to interpret (14c) as an expression of doubt.</Paragraph>
    </Section>
    <Section position="3" start_page="4" end_page="7" type="sub_section">
      <SectionTitle>
3.3 Contextual Knowledge
</SectionTitle>
      <Paragraph position="0"> An agent can infer from a dialogue many of the beliefs of the other participant.</Paragraph>
      <Paragraph position="1"> These acquired beliefs about the other participant's beliefs form one kind of contextual knowledge that can be used as evidence for the beliefs listed above. In addition, contextual knowledge determines the salience (or degree of prominence) of propositions at the current point in the dialogue, and salience is a factor that constrains the interpretation of coherent discourse actions. Consider the first three utterances in the dialogue shown in Figure 2. EA's acceptance of CA's telling of the proposition that Dr. Smith is teaching CS360 establishes the mutual belief that CA believes that Dr. Smith is teaching CS360 and thus provides evidence for the first belief; 5 in addition, the proposition that Dr. Smith is teaching CS360 becomes salient and is added to the dialogue context. Thus, while an utterance such as (12a) (12)a. EA: Doesn't Dr. Smith usually teach theory courses? might be used following (11) to express doubt at the statement that Dr. Smith is teaching CS360, it cannot be used following (11) to express doubt at the proposition that Dr. Smith teaches CS410 because 1) there is no reason for EA to believe that CA has any belief in the proposition that Dr. Smith teaches CS410, and 2) the proposition that Dr. Smith teaches CS410 is not salient at this point in the dialogue.</Paragraph>
      <Paragraph position="2"> In addition, contextual knowledge plays two other roles in the recognition of discourse acts. First, in the case of expressions of doubt, contextual knowledge distinguishes propositions that have not yet been accepted by the speaker and thus are open for rejection. Consider again the dialogue in Figure 2. After (13), there are two propositions that have not yet been accepted by EA and are thus open for rejection  by EA. If EA were to continue with (14b), repeated below, (14)b. EA: Isn't Dr. Smith a theory person? then EA would again be expressing doubt at the proposition that Dr. Smith is teaching CS360 and would have implicitly conveyed acceptance of the proposition that 5 Note that here EA is only accepting CA's felicitous telling of the proposition, but EA is not adopting the proposition as one of his own beliefs.  Computational Linguistics Volume 25, Number 1 Dr. Smith is not on sabbatical. Thus, as the conversation continues, only one proposition would remain open for rejection: the proposition that Dr. Smith is teaching CS360. This claim is supported by a combination of 1) the stack paradigm (Polanyi 1986; Reichman 1978; Grosz and Sidner 1986; Litman and Allen 1987), which treats topic structure as following a stack-like discipline; 2) focusing heuristics (McKeown 1983) that suggest that if a speaker has more to say about a topic, then he should do so before moving back to a topic deeper on the stack; and 3) the notion of implicit acceptance (discussed in Section 4.6) that argues that passing up the opportunity to reject an assertion in a collaborative dialogue communicates acceptance of it.</Paragraph>
      <Paragraph position="3"> Second, contextual knowledge orders propositions according to their relative salience in the current dialogue. This salience can be used to arbitrate among discourse acts for which there is equivalent evidence. Consider again the dialogue in Figure 2 and suppose that EA had continued with (14d).</Paragraph>
      <Paragraph position="4"> (14)d. EA: But isn't Dr. Smith an excellent teacher? Here we have a clue word suggesting an expression of doubt, but the speaker could be expressing doubt either that Dr. Smith is not on sabbatical or that Dr. Smith is teaching CS360. In both cases, we lack evidence for the third speaker belief. Contextual knowledge suggests that, all other things being equal, the proposition being doubted is the proposition that Dr. Smith is not on sabbatical, since it is the most salient proposition that is open for rejection at this point in the dialogue. Thus, contextual knowledge arbitrates when equivalent evidence is available for several specific discourse acts.</Paragraph>
    </Section>
    <Section position="4" start_page="7" end_page="7" type="sub_section">
      <SectionTitle>
3.4 Summary
</SectionTitle>
      <Paragraph position="0"> In addition to the requisite speaker beliefs being plausible and the constraints on the discourse act being satisfied (such as the constraint that a proposition be salient at the current point in the dialogue), certain discourse acts require additional evidence for their recognition. Two kinds of evidence that may be used in recognizing discourse actions are 1) evidence (such as a clue word) for a generic discourse act, and 2) evidence that a speaker holds the requisite beliefs for performing a particular discourse act.</Paragraph>
      <Paragraph position="1"> Evidence for these beliefs can come from linguistic, world, or contextual knowledge.</Paragraph>
      <Paragraph position="2"> Although we have illustrated each of these knowledge sources by showing how they might provide evidence for one of the requisite beliefs for expressing doubt, it should be noted that each knowledge source might also be used as evidence for other beliefs required for expressing doubt or for beliefs for other discourse acts. For example, although it does not generally arise in the kind of interactive dialogues that we are studying, world knowledge in the form of stereotypical beliefs might be used as evidence that a speaker believes that a hearer has some belief in the doubted proposition</Paragraph>
    </Section>
  </Section>
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