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<Paper uid="P86-1034">
  <Title>The Structure of User-Adviser Dialogues: Is there Method in their Madness? Raymonde Guindon Microeleetronies and Computer Technology Corporation - MCC</Title>
  <Section position="3" start_page="224" end_page="226" type="metho">
    <SectionTitle>
RESEARCH GOALS
</SectionTitle>
    <Paragraph position="0"> There are many unanswered questions about the nature of dialogue structures, about the validity and usefulness of the concept of a dialogue structure, about the role of the task structure in determining dialogue structure, and in the contribution of the task structure to focusing and anaphora resolution. For example, the precise mechanisms to determine the initial focus and to update it on the basis of the dialogue structure are still unknown (Sidner, 1983).</Paragraph>
    <Paragraph position="1"> The goal of this paper is to find evidence for the validity of the notion of discourse structure derived from the task structure by: 1) describing a technique to derive the structure of dialogues and 2) validating the derived dialogue structure by three independent converging analyses: a) the distribution of non-pronominal and pronominal noun phrases b) the distribution of antecedents of pronominal and non-pronominal anaphors, and c) the presence of subdialogue boundary markers, If complete subdialogucs get into and out of focus and if subdialogues are conceived as contexts restricting the set of antecedents to be searched and tested during anaphora resolution, identifying the appropriate unit of discourse corresponding to these subdialogues is crucial.</Paragraph>
    <Paragraph position="2"> One phenomenon that should have correspondence to the dialogue structure is the distribution of non-pronominal and pronominal noun phrases. Non-pronominal noun phrases can be used to introduce new entities in the dialogue or to reinstate into focus a previous dialogue entity out of focus. In other words, non-pronominal noun phrases are used to indicate topic shifts. As a consequence, they should tend to occur more frequently at the beginning of the subdialogues than later in the subdialogues. On the other hand, pronominal noun phrases are used to refer to entities currently in focus. In other words, pronominal noun phrases are used to indicate topic continuity. As a consequence, they should tend to occur less frequently in the first sentence of a subdialogue but more frequently in subsequent sentences.</Paragraph>
    <Paragraph position="3"> Empirical evidence for these claims are presented in Guindon (1985). She found that anaphora resolution time is faster for pronominal noun phrases whose antecedents are in focus than for those whose antecedents are not in focus. On the other hand, she found faster anaphora resolution time for non-pronominal noun phrases whose antecedents were not in focus than for those whose antecedents were in focus. In other words, the form of the anaphor signals whether the antecedent is in focus (as when the anaphor is pronominal) or not in focus (as when the anaphor is non-pronominal). Grosz, Joshi, and Weinstein (1983) have made similar claims about the role of non-pronominal definite noun phrases and pronominal definite noun phrases.</Paragraph>
    <Paragraph position="4"> In linguistics, Clancey (cited in Fox, 1985) found that the use of definite non-pronominM noun phrases was associated with episode boundaries. Psychological evidence has shown the special status in memory for certain sentences in discourse found at the beginning of paragraphs. Sentences which belong to the macrostructure (i.e. gist) of the discourse have been shown to be recognized with more accuracy and faster than sentences belonging to the microstructnre (Guindon and Kintsch, 1984).</Paragraph>
    <Paragraph position="5"> Macrostructure sentences are by definition more abstract and important than microstructure sentences. They express a summary of the or part of the discourse. The macrostructure sentences tend to be the first sentences in paragraphs and be composed of non-pronominal definite noun phrases (van Dijk and Kinstch, 1983).</Paragraph>
    <Paragraph position="6"> Linde (1979) observed the distribution of it and that in descriptions of houses or apartments. She found that shifts in focus were associated with change in the room described. The pronoun it was used to describe objects in focus either associated with the room then described or to the entire apartment even when the apartment itself had not been mentioned for many sentences. The pronoun that was used either to refer to an object outside the focus or to an object in focus when the description of the object was in contrast with another description. Grosz (1977) observed a similar use of the pronoun it in her dialogues to the use of it in Linde's dialogues.</Paragraph>
    <Paragraph position="7">  In summary, the most important sentences, often at the beginning of new paragraphs, tend to be composed of full definite noun phrases. These sentences often introduce a new discourse entity or reinstate a former one which was out of focus, creating a topic shift. Sentences which are nsubordinatedh to the most important sentence in the paragraph tend to be composed of pronouns and signal topic continuity.</Paragraph>
    <Paragraph position="8"> Another clue to dialogue structures is the distribution of antecedents of anaphors. Given that pronominals are used to refer to important or recent concepts (Guindon, 1985), the distribution of antecedents of pronominal anaphors should cluster in the current subdialogue (i.e. recency or importance), its parent (i.e. importance and recency), and the root subdialogue (i.e.</Paragraph>
    <Paragraph position="9"> importance). On the other hand, because non-pronominal anaphors are more informative than pronominal anaphors they may refer to antecedents that are more widespread in the dialogue, that is, antecedents that are not as recent or as important.</Paragraph>
    <Paragraph position="10"> Another obvious clue is the presence of reliable boundary markers for different subdialogue types. Some of these markers have been reported by Grosz (1977), Reichman (1981), and Polanyi and Scha (1983). The boundary markers found in our subdialogues should agree with those found in these previous analyses and extend them.</Paragraph>
    <Paragraph position="11"> Derivation of a dialogue structure on the basis of the task structure An important prerequisite in the interpretation of user-adviser dialogues is to analyze the task the users are trying to perform. A task analysis is a detailed description of the determinants of the user's behaviors arising from the task context. The first step in performing task analysis is to identify the objects involved in the task. In our case, these objects are vectors, matrices, rows, columns, variables, variable labels, etc. The second step is to identify all the operators in the task which when applied to one or more objects changes the. state of the completion of the task. In our case, these operators are function calls (e.g. mean, variance, sort), subsetting values from vectors, listing of values, etc. Of course, not every operator applies to every object. A third step is to identify the sequence of operators which would produce a desired state (the goal - e.g. the problem solved) from an initial state. Such a task analysis can be performed at many levels of abstraction, from high-level conceptual operators to low-level physical operators. The desired level of abstraction depends upon the level of abstraction of the behaviors that one wants to account for. Usually, the more complex or cognitive the task modelled, the more abstract or coarse the operators selected. In such case, the operators will reflect the specifics of the task environment, such as, vectors, matrices, screen, keyboard. The finer the grain of analysis, the more the operators are associated with basic motor, perceptual, or cognitive mechanisms. Since the task we are trying to model is quite cognitive in nature - solving statistical problems with an unfamiliar statistical package - an appropriate level of analysis seems to be at the level of the so-called GOMS model (Card, Moran, and Newell, 1983). GOMS stands for: (1) a set of Coals; 2) a set of Operators; 3) a set of Methods for achieving the goals; 4) a set of Selection rules for choosing among competing methods for goals.</Paragraph>
    <Paragraph position="12"> In the notation used in our examples, we have used a slightly different terminology and have used the term action instead of operator and use the term plan instead of method. We have also used the terms prerequisites, constraints, and meta-plans from artificial intelligence. The notion of meta-plans allowed us to account for the presence of clarification and acknowledgement subdialogues (see Litman and Alien, 1984) that could not be accounted directly by the task structure.</Paragraph>
    <Paragraph position="13"> We will now describe how the task structure was used in deriving the dialogue structure. Goal or plan subordination arises from the plan decomposition into subplans or from unsatisfied prerequisites. In a task structure, plans are composed of other plans themselves, leading to a hierarchical structure. In other words, a subgoal to a goal can arise from a plan decomposition into subplans or from the prerequisite conditions which must hold true before applying the plan. Here are the coding decisions used in deriving the dialogue structure: * If the user initiated a subdialogue consisting of the statement of a plan or of a goal, the subdialogue would be &amp;quot;inserted&amp;quot; in the task structure at the location of the plan described.</Paragraph>
    <Paragraph position="14"> * If the user initiated a subdialogue consisting of the statement of a subplan within the decomposition of its parent plan, the subdialogue would be &amp;quot;inserted&amp;quot; in the appropriate daughter subplan of the parent plan in the task structure.</Paragraph>
    <Paragraph position="15"> * If the user initiated a subdialogue consisting of a subplan arising from an unsatisfied prerequisite of a plan, then the subdialogue would be &amp;quot;inserted&amp;quot; as a daughter of the subdialogue associated with the plan.</Paragraph>
    <Paragraph position="16"> Clarification subdialogues arise from the restrictions on the meta-plans that the participants can use when they cannot achieve one of their plans: In our study, they must ask help to the adviser aloud. The meta-plan, ASK-ADVISER-HELP, itself has prerequisites, one of them being that the linguistic communication be successful. This leads to the linguistic clarification subdialogues that occur when there are ambiguities in the message that need to be resolved by requesting disambiguating information from the adviser. Another consequence of the meta-plan ASK-ADVISER-HELP is the presence of acknowledgement subdlalogues whereby participants ensure that the communication is successful by acknowledging that they have understood the message.</Paragraph>
    <Paragraph position="17"> Let's continue describing the coding scheme:  subordinated to the subdialogue containing the utterance for which clarification is requested.</Paragraph>
    <Paragraph position="18"> * Since we are not fully modeling the user's task, subdialogues regarding the participants' behaviors as a subject in a study were ignored.</Paragraph>
    <Paragraph position="19">  * Since knowing the required statistical formula and knowing how to use the console were required to solve all the problems, these prerequisites were not always encoded explicitly in the task structure. Nevertheless, the clarification and acknowledgement subdialogues regarding statistics and the use of the console were subordinated to the subdialogue associated with the plan for which these clarifications were necessary to obtain.</Paragraph>
  </Section>
  <Section position="4" start_page="226" end_page="226" type="metho">
    <SectionTitle>
DATA COLLECTION
</SectionTitle>
    <Paragraph position="0"> Overview of Data Collection Method Three novice users had basic knowledge of statistics. They had to use an unfamiliar statistical package to solve five simple descriptive statistics problems. There were two main restrictions imposed on the strategies employed to solve the problems: 1) the only source of information was the adviser; 2) all requests for information had to be said aloud. These restrictions were considered as restrictions on the mcta-plans available to the participants when unable to solve the problems. The participant, the adviser sitting to his/her right, and the console were videotaped.</Paragraph>
    <Paragraph position="1"> Coding of the Dialogues Each subdialogue was segmented into subdialogues which appeared to be the execution of a plan to satisfy a goal of the user or the adviser on the basis of the task structure.</Paragraph>
    <Paragraph position="2"> In addition to segmenting the dialogue into subdialogues, the relations between subdialogues were determined. One source of such relations is the decomposition of a total task into subtasks to be performed in some order. This decomposition is called the task structure (see Grosz, 1977) as described previously. Two important relations are subordination and enablement.</Paragraph>
    <Paragraph position="3"> Consider a dialogue occurring while performing a task, such as baking a cake, composed of three subtasks, (1) measure ingredients, (2) mix ingredients, (3) put the mixed ingredients in the oven. Subtasks 1, 2, and 3 are said to be subordinated to the task of baking a cake. Moreover, subtask 2 must precede subtask 3. Subtask 2 is said to enable subtask 3. The subdialoguss that would be instrumental to the execution of these subtasks would stand in the same relations.</Paragraph>
    <Paragraph position="4"> However, the decomposition of the task structure was not the only source of subordination and enablement relations between subdialogues. Clarification and acknowledgement subdialogucs even though they did not correspond to a subtask in the task structure were subordinated to the subdialogue introducing the clarified and acknowledged concept respectively.</Paragraph>
    <Paragraph position="5"> The coder then analyzed the distribution of non-pronominal noun phrases and pronominal noun phrases throughout the dialogue. The coder also noted words and phrases occurring at the boundaries of the subdialogues and mapped the distribution of the antecedents of pronominal and non-pronominal anaphors.</Paragraph>
  </Section>
  <Section position="5" start_page="226" end_page="227" type="metho">
    <SectionTitle>
ANALYSIS OF THE DIALOGUES
ANALYSIS OF THE USERS' TASK
</SectionTitle>
    <Paragraph position="0"> Three main types of subdialogues have been encountered associated with each aspect of the task described above : 1. Plan-goal statement subdlalogues occur when the user describes a goal, or a plan, or the execution of actions composing the plan This type of subdialogue may be an adjunct to the goal or plan because expressing them verbally might not be essential for their satisfaction or realization (though expressing them verbally helps the adviser understand the user).</Paragraph>
    <Paragraph position="1"> 2. Clarification subdialogues occur when the user requests information from the adviser so that the user can satisfy a goal. In this study, these subdialogues arise from the constraints on the type of meta-plans available, ASK-ADVISER-HELP. There are two main types of clarification subdialogues: 1) those concerning the determination of goals and plans of the user (e.g., &amp;quot;What should I do next?&amp;quot;, &amp;quot;How do I access a vector?&amp;quot;); 2) those concerning the arguments (or objects) in goals and plans (e.g., &amp;quot;What is a vector?&amp;quot;). In some cases, the clarification subdialogues arise from the prerequisite on the recta-plan, that is, assure mutual understanding. For example, the user will verify that he/she has identified the correct referent for an anaphor in the adviser's utterances.</Paragraph>
    <Paragraph position="2">  3. Acknowledgement subdialogues occur when the user informs the adviser that he/she believes that he/she has understood an explanation. They arise from  the prerequisite on the recta-plan, that is, assure mutual understanding.</Paragraph>
    <Paragraph position="3"> A small subset of the graphical representation of a simplified subtask structure and of dialogue segmentation and structure is given in Figure 1 to show how the task structure partially influences the dialogue structure.</Paragraph>
  </Section>
  <Section position="6" start_page="227" end_page="227" type="metho">
    <SectionTitle>
DISTRIBUTION OF NON-PRONOMINAL
AND PRONOMINAL NOUN PHRASES
</SectionTitle>
    <Paragraph position="0"> Non-pronominal noun phrases play a role in indicating and realizing topic shifts in a dialogue. Since new subdialogues are assumed to correspond to topic shifts, one can predict that non-pronominal noun phrases will tend to occur more frequently at the beginning of subdialogues than later in the subdialogues. On the other hand, pronominal noun phrases play a role in indicating and realizing topic continuity in a dialogue. Since new topics are introduced at the beginning of new subdialogues and developed in the following sentences, one can predict that pronominal noun phrases will tend to occur more frequently after the first sentence in the subdialogues. As can be seen in Table 1, there is a clear trend for the number of non-pronominal noun phrases to decrease as the subdialogue progresses, especially for the most frequent subdialoguc lengths (i.e., 2 and 3 sentences), but less marked for the most infrequent subdialogue lengths (i.e., 4 and 5 sentences).</Paragraph>
    <Paragraph position="1"> Moreover, there is a clear increase in the number of pronominal noun phrases from the first sentence to the second sentence in the subdialogues, though again less reliable for the least frequent subdialgue lengths (i.e., 4 and 5 sentences). A complete statistical analysis of these data is presented in Guindon, Sladky, Brunner, and Conner (1986).</Paragraph>
    <Paragraph position="2">  The observed distributions oPS non-pronominal and pronominal noun phrases follow the predictions arising from previous work in linguistics and psychology. Because this analysis was performed independently of the dialogue segmentation and subordination, it is a converging analysis and it supports the derived dialogue structure on the basis of the task structure and the users' and adviser's plans and goals. This analysis supports the value of the concept of a dialogue structure and also support our proposed scheme to derive such dialogue structures.</Paragraph>
  </Section>
  <Section position="7" start_page="227" end_page="227" type="metho">
    <SectionTitle>
DISTRIBUTION OF THE ANTECEDENTS
OF ANAPHORS
</SectionTitle>
    <Paragraph position="0"> The subdialogues were indexed as shown in Table 2. The current subdialogue, labelled N, is the location of the anaphor to be resolved. All subdiMogues are indexed relative to the current subdialogue N. Thus, the node N-1 immediately dominates N, the node N-2 dominates N-I, and so on. The nodes subordinate to each of the nodes dominating N are indexed beginning with the left-most node and proceeding rightward. Thus, if N-1 is the first node dominating N, the left-most node subordinate to N-1 will be</Paragraph>
    <Section position="1" start_page="227" end_page="227" type="sub_section">
      <SectionTitle>
Anaphoric - Pronominal Noun Phrases
</SectionTitle>
      <Paragraph position="0"> Pronominal anaphors are used to refer to discourse entities that are in focus. Such entities should be either recent or of primary importance in the dialogue, Figure 2 represents graphically the distribution of the antecedents of pronominal noun phrases with a band, with highest frequencies shown with the widest bands. For sake of brevity, the exact frequencies are not reported here but can be found in Guindon, Sladky, Brunner, and Conner (1986).</Paragraph>
      <Paragraph position="1"> Figure z shows that the majority of pronominal antecedents are located in the current subdialogue, with their frequency decreasing as distance from the anaphor increases. The current subdialogue contains recent antecedents. Then, they are most frequently found in the parent subdialogue which contains important and recent antecedents. Finally, a few pronominal anaphors (i.e. it) have their antecedent (i.e., the statistical package) found in the root subdialogue which contains important antecedents. Grosz (1977) also observed the use of it to refer to an important concept that had not been mentioned for many sentences. These data demonstrate the existence of constraints at the dialogue level on the distribution of the antecedents of</Paragraph>
    </Section>
  </Section>
  <Section position="8" start_page="227" end_page="228" type="metho">
    <SectionTitle>
ANTECEDENT DISTRIBUTION
</SectionTitle>
    <Paragraph position="0"> pronominal anaphors: most antecedents are located in the current subdialogue or in its immediate superordinate and a few antecedents co-specifying the main topic(s) of the dialogue are located at the root of the dialogue.</Paragraph>
    <Paragraph position="1">  These data strongly suggest that recency plays a role within the current subdialogue, but also that another factor must be invoked to explain the high frequency of antecedents observed in N-1 and in the root subdialogue. This other factor is topicality or importance (Guindon, 1985; Kintsch and van Dijk, 1978). A parent subdialogue describes information that is important to the information described in a subordinate subdialogue.</Paragraph>
    <Paragraph position="2"> Moreover, the antecedent statistical package was located at the &amp;quot;root&amp;quot; subdiMogue of the dialogue structure. In other words, it was one of the most important concepts mentioned in the dialogue and because of its importance stayed in the user's and adviser's short-term memory during the complete dialogue and could be referred to by using a pronoun. The allocation of short-term memory during discourse comprehension corresponds to the concept of attentional state (Grosz and Sidner, 1985) and is described in more detail in Guindon (1985).</Paragraph>
    <Paragraph position="3"> The task structure and the user's meta-plans correspond to the intentional structure described by Grosz and Sidner (1985). Note that the segmentation of the task into subtasks direct the segmentation of the dialogue into subdialogues and is also a determinant of focus shifts and the attentional state. The antecedent distribution for pronominal anaphors is consistent with the dialogue structure derived from the user's plans and goals and describe principled and psychologically valid constraints on the use of pronominal anaphors over an extended dialogue. As a consequence, the validity of the derived dialogue structure is increased.</Paragraph>
    <Section position="1" start_page="228" end_page="228" type="sub_section">
      <SectionTitle>
Anaphoric - Non-pronominal Definite Noun
Phrases
</SectionTitle>
      <Paragraph position="0"> Selecting the proper antecedent for a non-pronominal definite noun phrase anaphor is less difficult than for pronominal anaphor since more semantic information is provided for matching the description of the antecedent. For this reason we would expect the distribution for antecedents of non-pronominal definite noun phrases to be far less constrained than the distribution for pronominal noun phrases. Figure 2 shows that this is the case.</Paragraph>
      <Paragraph position="1"> Definite noun phrase antecedents range over every dominant node N-1 through N-5 and over a few left-branching subordinate nodes.</Paragraph>
      <Paragraph position="2"> Nevertheless, there is a strong tendency for antecedents to be locally positioned in N and N-1. Their distribution is consistent with the derived dialogue structure on the basis of an analysis of the task and an analysis of the users' and adviser's plans and goals.</Paragraph>
    </Section>
  </Section>
  <Section position="9" start_page="228" end_page="228" type="metho">
    <SectionTitle>
BOUNDARY MARKERS
</SectionTitle>
    <Paragraph position="0"> The analysis of boundary markers revealed reliable indicators at the opening of subdialogues in adviser-user dialogues. This is shown in Table 3. The determined boundary markers were consistent with those found by Grosz (1977), Reichman (1981), and Polanyi and Scha (1983). The boundary markers can help identify three major types of subdialogues: I) plan-goal statement; 2) clarification; 3) acknowledgement. Acknowledgement subdialogues occur very frequently at the end of clarification subdialogues, also acting as closing boundary markers for clarification subdialogues.</Paragraph>
    <Paragraph position="1"> A more detailed analysis of the boundary markers is given in Guindon, Sladky, Brunner, and Conner (1986).</Paragraph>
    <Paragraph position="2"> A small subset of these markers for each type of discourse act is given in Table 3 (the symbol ~ &gt; means optional, &amp;quot;or&amp;quot; is indicated as \[ ( ) ( ) I, and ACTION means an instance from a class of actions).</Paragraph>
    <Paragraph position="3">  The boundary markers are part of the linguistic structure of dialogue, and so is the distribution of the non-pronominal and pronominal noun phrases. Both analyses are consistent with the derived dialogue structure on the basis of the task structure and the users' and adviser's plans and goals and they increase the validity of the derived dialogue structure. Both analyses also show that shifts in focus during discourse comprehension can be signalled in the surface form of the conversants' utterances. As a consequence, they can be capitalized upon by natural language interfaces.</Paragraph>
  </Section>
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