<?xml version="1.0" standalone="yes"?>
<Paper uid="W96-0511">
  <Title>Implementing an Integration of the Systemic Flowchart Model of Dialogue and Rhetorical Structure Theory</Title>
  <Section position="2" start_page="0" end_page="0" type="metho">
    <SectionTitle>
COMMUNAL Project (Lin, Fawcett and Davies
</SectionTitle>
    <Paragraph position="0"> 1993).2 The second is Fawcett and Davies' ~rogrammatic paper (1993), which describes ow an integration of RST and the SFM might be attempted, The purpose of the present paper is to give an account of an implementation of the point where the two models are integrated - including a new system network through which this is achieved. We see no reason why other contributions that draw on a broadly systemic functional approach to modelling RST relations, such as Vander Linden, Cumming and Martin (1993) and Maier and Hovy (1993), may not be integrated with the present proposals.</Paragraph>
    <Paragraph position="1"> 2. Some problems in relating RST to the SFM Fawcett and Davies (1993) provide summary descriptions of the two approaches, so we shall not replicate those descriptions here. That paper also discuases some of the possible difficulties in integrating the SFM and RST.</Paragraph>
    <Paragraph position="2"> Fawcett and Davies concluded: We do not expect a 'seamless join' between the two models to occur effortlessly; there are bound to be difficulties of many kinds as we explore possible ways of bringing the two models together. But, given the richness and flexibility of the descriptive and implementational tools available to us, it is an enterprise on which we can enter with an expectation of some measure of success.</Paragraph>
    <Paragraph position="3"> Here we shall report both the way in which we have successfully modelled the point in the overall discourse grammar at which RST and the SFM meet, and the surprising ease with which we were able to do it.</Paragraph>
    <Paragraph position="4"> For the Birmingham School of Discourse Analysis, a dialogue consists of a series of transactions, each of which is made up of a number of exchanges. These in turn have constituents called moves, and each move consists of one or more acts. Thus their model assumes that there is a rank scale relationship between these units (Halliday 196l). This concept is found in the SFM too.</Paragraph>
    <Paragraph position="5"> In RST, on the other hand, there is the potential for the unlimited recursion of structures consisting of a nucleus with a satellite in the relation of elaboration or reason, etc. In the integration of the two to be described here we model this as the recursion of acts within acts. The SFM model of discourse structure is both richer and at the same time more traditional than the types of structure built in RST. The main difference in 'richness' is that each node is labelled twice. It is shown as both an element of structure in the unit above, and by the name of the unit that fills it. Thus the concepts of 'nucleus' and 'satellite' are treated here as elements of structure. The SFM is more traditional in that its structure is based on 'constituency' rather than the concept of 'sister dependency', as in RST. This provides a richer and so more informative labelling, with the rhetorical relation shown as the class of act.</Paragraph>
  </Section>
  <Section position="3" start_page="0" end_page="43" type="metho">
    <SectionTitle>
3 A typical structure
</SectionTitle>
    <Paragraph position="0"> We will now look at a typical example of the sort of structure that occurs at the point where the rank-based structure of the SFM meets the potential recursion of RST relations - using for both a 'constituency' approach that has at each node both elements and units.</Paragraph>
    <Paragraph position="1">  act: act: act: act: inform background inform reason I II II II I I went to He'd agreed to It took us as we dissee Fred. discuss my a long agreed on paper with me. time, several points.</Paragraph>
    <Paragraph position="2">  at the point where RST and the SFM meet How is this structure generated? To see this, we must look at the new system network shown in Figure 2 - and also at Its associated realization rules, because it is through these that the chosen features are converted into structures. 4 How the structure is generated The discourse generator that we are about to describe is called GENEDIS, because it GENErates DIScourse (For details see Lin et al. 1993.) Many of its choices are guided by the goals set in the higher planning component, but much of the 'discourse potential' is captured here. As it enters the network in Figure 2, it knows that it has the goal of filling the Respond element (hence 'R') of an exchange, and that it is to be uttered by Ivy (i.e. the system). The network operates in the following manner. We enter it at \[discourse unit\], and find that the probabilities in the initial system are set 100% to \[move\]. (On (re-entry to the network to fill out the lower part of the tree, however, this choice will be reversed.) As you will see if you look at the realization rules, the selection of \[move\] inserts first the unit 'move' into the structure, and then locates the element nucleus (N) at Place 2 in that move's structure. (We shall shortly see why it is at Place 2 rather than Place l.) We now encounter two 'simultaneous' stems. In the MOVE CLASS system, NEDIS typically choos~-s one of the five major classes of move. The realization rule on each of these inserts this into the structure (the relationship of 'class' being shown by a colon). Notice that the categories that get inserted into the growinu structure may have similar or even identical labels to the features in the network. In principle the two are separate, but there is little point in multiplying terms unnecessarily. In the lower system, i.e. MOVE_COM-PLEXITY, our choice is \[with_satellite_m\]. (Lack of space prevents us from describing the effects of choosing \[simplem\] or \[co_ordinatedm\], but the rules given cover the former.) However the typical choice - and the most interesting one - is \[with satellite m\]. The choice of this feature aff~ts the structure in four ways. First, its realization rule (0.4) rovides for re-entry to the network to fill N. is this fact that provides for the recursion typical of RST relations in the present framework, as we shall shortly see.</Paragraph>
    <Paragraph position="3"> But this feature also leads on to two further simultaneous systems: one for RHETORICAL RELATIONS and a second for SATELLITE THEMATIZATION. We will take the latter first. The concept of 'thematizing' an element in the structure of a unit comes from systemic functional grammar, where it is mainly associated with the clause. We use the same term here because the motivation is similar in both. Typically, the satellite follows the nucleus, but the different types of rhetorical relation have different typicalpatterns in this respect. So how does GENEDIS know which to choose? The answer lies in the upper system, and the entry to this is the third effect of choosing \[with_satellitem\]. As you will see, the features here are precisely those of the rhetorical relations of RST. But notice that these features have attached to them same pass (sp) preference resetting rules (i.e. these rules are not realization rules). It is these that express the likelihood that the satellite will precede or follow the nucleus - as the sp rules below the network show. One advantage of using probabilities on features in systems is that they can be varied, e.g. for different types of genre {cp. the. prevalence of thematized 'purposes' m certain types of instructions). In some cases the probabilities are absolute, as in our case, where the sp rule on \[elaboration\] makes it 100% certain that the S will follow.</Paragraph>
    <Paragraph position="4"> In any given instance, of course, the Performer may have a reason to thematize a satellite that overrides the probabilities, but in a sophisticated model he/she should be able to set this against the knowledge of the general probabiffties for a ,ziven type of rhetorical relation. The finaVeffect of selecting \[withsatellite _m\] is to provide that the network will be reentered to fill S, as in Rules 0.5 and 0.51.</Paragraph>
    <Paragraph position="5"> We have now generated all of the structure of the move. This part of the network is nonrecursive, but as we now re-enter the network to generate the acts that will fill the N and S of the move, we meet a recursive system network.</Paragraph>
    <Paragraph position="6"> The recursion is modelled through the realization rules; a new layer of structure is added by each re-entry to the network. And the potential for recurslon is, in principle, infinite. On re-entry to the network to fill N, the preferences have been reset to \[act\] and \[nucleus _act\]. Similarly, on re-entry to fill S they are reset to \[act! and \[satellite_act\]. Rule 0.7 inserts the unit act' in both cases. The class of act to fill N comes from the network tor ACT_CLASS, and in our case Rule 0.8 inserts 'inform' after 'act'. It is Rule 0.71 on \[satellite act\] that determines what the class ef the act filling S will be. Thus, since in our case \[elaboration\] has been chosen on the 'mother'  if ~,ith_satdilite_a then-N @ 2, for N prefer \[act, nucleus_act, for N re_enter_at discourse_unit. 0.5 : satellite thematized : S @ 1, for S prefer \[act, satellite_act, for S re_enter_at discourse_unit. 0.5t : satellite_unthematized : S @ 3, for S prefer \[act, satellite_act, for S re_enter_at discourse_unit. 0.7: act:act. 0.71 : satellite_act : if on_mother_pass elaboration then act_class elaboration, if on_mother_pass purpose then act_class purpose, if on_mother_pass reason then act_class reason, if on_mother pass background then act class background. 0.8 : inform: act_class inform. 0.87 : exclamation: act_class exclamation.  Model of dialogue structure with the relations of Rhetorical Structure Theory  pass through the netw, ork the class of the act will be an elaboration.</Paragraph>
    <Paragraph position="7"> The final two systems are ACT_COM-</Paragraph>
  </Section>
  <Section position="4" start_page="43" end_page="43" type="metho">
    <SectionTitle>
PLEXITY and ' SATELLITE THEMATIZ-
ATION - and it is these that ~ovide for the
</SectionTitle>
    <Paragraph position="0"> recursion. As you will see, the first is entered from both \[nucleus_act\] and \[satellite_act\].</Paragraph>
    <Paragraph position="1"> And one of its features is \[with_satellite_a\], whose Rule 0.4 provides for re-entry to fill N.</Paragraph>
    <Paragraph position="2"> * . , * . O t Finally, it leads on to choices m themauzm_ the S, and to the realization rules that proviffe for re-entry - like those for the S in a move.</Paragraph>
    <Paragraph position="3"> Thus the network and realization rules together provide for the recursive embedding of acts with further acts at either N or S or at both, In, this way,,then, we do indeed move virtually seamlessly from the SFM structure to RST relations.</Paragraph>
  </Section>
class="xml-element"></Paper>