<?xml version="1.0" standalone="yes"?>
<Paper uid="W93-0214">
  <Title>Towards stratification of R,ST</Title>
  <Section position="2" start_page="0" end_page="52" type="abstr">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Moore and Pollack have recently given an analysis of R.ST relations in tel'mS of intentional versus informational levels of discourse \[5\]. Accol'ding to their (convincing) analysis, presentational RST relations correspond to the intentional level of discourse and subject matter relations to the inlbrmational level. For each text there shouhl exist two RST analyses: one containing only presentational relations and the other containing only subject matter relaLtions. Mann and Thoinpson had discussed multiple analyses in RST (Ill, l)P. 2(i-30), stating that a presentational analysis is the only analysis when l)oth presentational and sul)ject-matter relation definitions are satisfied between a given pair of text spans. In their view, the l)resentational analysis is chosen as correct since it describes the changes in the bearer's system of beliePSs, i.e. provides deeper insights into discourse goals. Moore and Pollack, however, argue that these two a.nalyses should not compete; instead, &amp;quot;a complete model of discourse structure lnust maintain both levels of relation&amp;quot;.</Paragraph>
    <Paragraph position="1"> In this paper we take this argument one sma.ll step further and suggest a way these two levels might be organized into a stratified structure. Our discussion here ha.s a very narrow focus anti does not attempt to answer such iml)ortaut (luestions a.s whether the RST collection of presentational relations is exhaustive and adequate \[br describing a.ll possible lilt(rational structures.</Paragraph>
    <Paragraph position="2"> 2 Analogy with &amp;quot;Meaning&amp;quot; vs. &amp;quot;Means&amp;quot; in MTT In Meaning-Text theory (MTT), when there are two (o1' more) alternative analyses of text which (according to intution) belong to distinct levels of representation, one should ask whether one of tlmm can be seen as a means of expressing the other. Moore and Pollack argue for co-existence of intentional (presentational) and infornlatiolLa\] (subject matter) allalys(,s, but they do not attempt to describe the relationship between them. They show that there is no one-to-one mapping between presentational and subject matter relations, and moreover, that the presentational and subject matter analyses may have different structures (e.g., the i)resentational and subject matter relations may have opposite directionality, \[5\], pp. 542- 543). Their conclusion is that there is no easy way to relate these two levels.</Paragraph>
    <Paragraph position="3"> Froln the viewpoint of MTT, however, the intentional vs. inibrma.tiona.l dichotomy observed by Moore and Pollack appears quite natural. An a.nalogy ca.n be seen with the relationshil~ between the semantic and deep syntactic levels in MTT: semantic relations are in a many-to-many corre-Sl)ondence with (leep syntactic relations. Moreover, there is no isomorl~hism or even preservation  of structure between a semantic graph and a deep syntactic tree which expresses it. For exaxnple, on the semantic level, an adverb such as oftcn is typically analyzed a.s a predicate whose argument (i.e., dependent) is the remaining sentence graph. On the (deep) syntactic level, the same adverb is a dependent of the main verb. Thus the direction of dependency can easily change as one passes from semantics to syntax.</Paragraph>
    <Paragraph position="4"> Following this analogy, we propose to consider the informational level of discourse as a means of expressing the intentional level. Intuitively, this seems quite l)lausil)le because inlbrming the hearer about informational relations 1)etween discourse elements can hardly be considered a self-sufficient goal. Moore and Pollack stress that the intentional level is the primary one since it describes the speaker's strategy to achieve her intentional goal.</Paragraph>
    <Paragraph position="5"> In keeping with MTT methodology, to give substance to a claim of separate strata, one must produce a system of rules that map the relations of the &amp;quot;meaning&amp;quot; level to the relations of the &amp;quot;means&amp;quot; level. Each &amp;quot;meaning&amp;quot; relation can map to many &amp;quot;means&amp;quot; relations (or comi)inations of such relations) and vice versa, one and the same &amp;quot;means&amp;quot; relation can al~pe~.r in more than one mapping rule. Ea.ch rule describes the contextual conditions tbr its a.pl)lic;l.tion in enough detail to justify the distinction between various &amp;quot;means&amp;quot;, if such exist.</Paragraph>
    <Paragraph position="6"> At the moment, we can give only a few examl)les of such real)ping rules, olle of which we \[)resent below. Nevertheless, we present this very preliminary ana.lysis ti),&amp;quot; l),H'l)()ses of discussion, in the belief that work in discourse rel)resentation is crucial for text generation theC/)ry and apl)lications. A stratificational view has significant iml)licatioHs. ()lie of these is to eliminate lineal&amp;quot; order from the description of intentional RST relations. Note th~l.t in RST a givel, intentional relati~m may hold between two text segments a.l)pearing in either order provided th~l.t apl~tol)riate discourse connectives are used. In our view, linear order and, correspondingly, discourse connectives should appear only on the informational level. A1)stract intentional relations express only the dependellcies between propositions, not the lexical or &amp;quot;syntactic&amp;quot; artifacts associated with the means of their expression.</Paragraph>
  </Section>
class="xml-element"></Paper>