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<Paper uid="C86-1008">
  <Title>A TWO-LEVEL DI~ REPRESENTATION 1</Title>
  <Section position="4" start_page="42" end_page="44" type="metho">
    <SectionTitle>
3. %~E COMV~\]NICATIVE COMPONENT
</SectionTitle>
    <Paragraph position="0"> The following two assumptions form the basis for a pairing of a dialogue planning mechanism with elexents of the clialogue description system: dialogue participants always have two cooperating types of goals, substantive real life goals (Sgoals), which determine &amp;quot;what to say&amp;quot;, and linguistic/communicative goals (C-goals), which determine &amp;quot;how to say it&amp;quot;. No relation of necessity seems to hold between them. In fact, in most cases there are many different ways of expressing the same goal.</Paragraph>
    <Paragraph position="1"> it is possible to identify hierarchical relations between goals and subgoals both for substantive and communicative goals. However, in the high level dialogue description system units S-goals see/~1 to be more important, while at the low levels C-goal seem to prevail.</Paragraph>
    <Paragraph position="2"> The highest level of the discourse structure is the transaction. Given that the dialogue as a whole is a means of effecting the high-level goals of one or other of the participants, we can functionally define transaction as the unit of dialogue concerned with effecting these high-level goals.</Paragraph>
    <Paragraph position="3"> At the highest lewi.~l of the dialogue's goal structure the dominant goals motivating the transaction are those concerned with the substance of the dialogue, not the means by which the substance is conveyed. As we move down this hierarchy it is possible to discern a bifurcation of goals into one group concerned with the substance of the dialogue, and the other concerned with communication of this substance. These are the S-goals and C-goals (or more properly, S and C subgoals) mentioned above.</Paragraph>
    <Paragraph position="4">  A transaction is always motivatedby a general goal such as seek information, make a train journey (Allen, 1982), make a reservation. The social context, for example the relation between speaker and hearer or simply a social convention, can suggest rhetorical choices. Among these might be the direct stating of the general goal, the indirect revelation ofthe general goal by several related questions, the questioning of a system's general capabilities before asking, and so on.</Paragraph>
    <Paragraph position="5"> Essentially, exchanges can be thought of as the topic-bearing elements of the dialogue. New topics are introduced by either an EB-exchange (explicit boundary), a C-exchange (conversational) with an opening move as its first move, or a C-exchange with a challenge as its first move. Topics that have been discussed prior to the most recent challenge are re-introducedby a C-exchange with a re-opening move as its first move. Topics that have been discussed less recently are re-introduced by means of an EB-exchange containing a sketching move.</Paragraph>
    <Paragraph position="6"> There is, therefore, a strong connection between the exchange structure of the transaction and the pattern of topic-shifts in the dialogue. These topic-shifts, in turn, are related to the conversant's shifting goal structure. This is especially true in task-oriented dialogues, where the component operations of the task are mirrored in the topic structure of the dialogue (Grosz, 1981). A general goal can be, therefore, split into a sequence of subgoals bof/n because the task consists in reality of a sequence of subtasks (Grosz, 1981) and because of rhetorical reasons. This gives a very special status to exchanges in our classification system. A transaction is in fact, divided into several exchanges determined either by the structure of the task to be carried out, or by rhetorical considerations, or by both. In particular, we should distinguish between two types of exchange: - a subtask exchange, which aims at reaching some substantive subgoal - an instrumental exchange, which aims at attaining some communicative (sub)goal, such as introducing the terms of the conversation, or clarifying some unclear substantive goal or subgoal.</Paragraph>
    <Paragraph position="7"> Every exchange is conloosed of moves and is, in most cases, opened by some form of topic shifting move and closed by a concluding move. Other sabcategories of exchanges can be found. However, a pattern of moves is associated with every exchange. At this level different rhetorical choices (motivated by C-goals) may appear in the form of different distributions of instrumental or nonclarifying exchanges within a transaction. The S-goals of an exchange can be computed from the interpretation of the utterances comprising it, utilising some notion of general focus (Sidner, 1979).</Paragraph>
    <Paragraph position="8"> At a lower level, the goals that motivate the moves are drawn equally from S-goals and C-goals. At the move level, the S-goal structure becomes less relevant to the sequence of moves. Moves are mostly rhetorical elements. They signal the pushing to a (new) topic (topic shifting and topic re-introducing moves), the continuation of a topic (topic  maintaining moves), and the popping of a topic (nonintroduction). null Pushing and popping are the opening and closing moves of an exchange. The coherence of the topic is to be expected within an exchange and should be perhaps checked from one move to the other. A topic shift is in itself a pushing move. The notion of topic probably coincides with the notion of focused goal.</Paragraph>
    <Paragraph position="9"> Moves serve as syntactic components of exchanges and every move is a step in a linguistic goal structure. Therefore, every exchange consists of a pattern of moves representing the communicative choices of the dialogue participants. In some cases, there is a correspondence between the S-goal associated with an exchange and some move (challenge). Also a communicative adherence between one move and the following should hold. Coherence means that the topic must be roughly the same, while adherence moans that the given move canbe followed only by a specific set ofmoves.</Paragraph>
    <Paragraph position="10"> Finally, an act is a limited linguistic act, uttered to effect very local communicative/rhetoric goals. In a dialogue most moves consists of a single act, but this does not. always hold. A distinction can be made at the act level between acts which are drawn from a limited class of utterances, and acts which are not limited in this way. We will call these closed and open classes, respectively. Most of the closed class items are associated with acts which subserve C-goals rather than S-goals. This is not too surprising since the items from the closed class do not usually convey substantive information but usually serve as go-ahead signals in a dialogue.</Paragraph>
    <Paragraph position="11"> Whereas the primary function of open class items is to convey task-relevant information.</Paragraph>
  </Section>
  <Section position="5" start_page="44" end_page="44" type="metho">
    <SectionTitle>
4. SYNTACTIC STRUCTURE AND GOAL STRUCTURE
</SectionTitle>
    <Paragraph position="0"> From the previous paragraph it has been clear that there is a different distribution of S and C-goals along the hierarchy of dialogue units. In particular, higher level units are more related to S-goals, while low level units are connected to Cgoals. null The model presented is intended to serve mainly descriptive and representational purposes. No definition is given of the process of inference of the goal structure from the syntactic structure of dialogue. However it is possible to imagine that such a process rely, among others, on - the functions assigned to ~ialogue subunits - the actions mentioned in any specific utterance.</Paragraph>
  </Section>
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