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<Paper uid="C96-2133">
  <Title>Multiple Discourse Relations on the Sentential Level in Japanese</Title>
  <Section position="3" start_page="788" end_page="789" type="metho">
    <SectionTitle>
2 Discourse Relations in Japanese
</SectionTitle>
    <Paragraph position="0"> As mentioned above, it is apparent in Japanese that a sentence can include a number of discourse relation elements (Fig. 1). Keeping track of the assumption that all discourse relations in a sentence take a wider scope than the other scope-taking elements in a sentence, we are confronted with the l Since the Verbmobil project deals with spoken languages, the unit treated is in reality not a sentence but an utterance which constitutes a turn in a dialogue and includes ellipsis mM other typical phenomena which need special treatments. Here, however, the linguistically abstract unit of sentence will be presupposed.</Paragraph>
    <Paragraph position="1"> next question which kind of relative scope holds among discourse relations. The treatment of discourse relations should thus be modified at least in these respects.</Paragraph>
    <Paragraph position="2"> A discourse relation is represented in LUD as a predicate with three arguments; the first one is a term for the type of the concerning discourse relation, the second one is an underspecified scope domain of the antecedent part, and the last one is another underspecified scope domain for the conclusion part. An underspecified scope domain is represented by a hole.</Paragraph>
    <Paragraph position="3"> In Japanese sentences, discourse relations occur in various grammatical positions. The sentence in Fig. 1 contains at least three different discourse relations. First, there is a topic relation which is expressed by a so-called topic phrase marked by wa. It is encoded in tile LUD as in (1) (of. Asher's elaboration relation (Asher, 1993)). In Japanese, the antecedent part can be syntactically determined, so far as the topic phrase is expressed with the topic marker. In Fig. 1, getsuyoubi amounts to this part.</Paragraph>
    <Paragraph position="4">  pressed by the auxiliary noda in the modality position of the verbal complex of the conclusion part of the sentence. Semantically, it is an subordinate relation of explanation. It consists of a functional noun for the senteutial nominalization no and the copula. The use of noda is dif\[crent from the norreal use of the copula in that it takes a temporalized sentence as a complement and, at the same time, lacks the argument of the copular predication. It is this lacking argument which makes up the conclusion part of the discourse relation (h6 in (2)). h5 will be bound to a DRS which is constructed out of the sentence subordinated to noda, that is, the whole sentence.</Paragraph>
    <Paragraph position="5"> Finally, a discourse relation expressed by a subordinate conjunction node can be found in Fig. 1, too (3). This form can be seen as a participle form (re-form) of noda mentioned above. Semantically, the meaning is restricted to explanation. Therefore, the term for the discourse relation type is basically the same as (2).</Paragraph>
    <Paragraph position="6"> Even taking these pieces of information into account, the scope relations both between wa and uoda and between wa and node seem to be underspecified, whereas noda always has scope over node. Since every discourse relation has two scope  domains, this observation leads to the following possibilities of scopal relations for Fig. 1.2 These scopal relations are at least theoretically able to  be forced onto the sentence in Fig. 1 (see See. 5). (4) wa (monday ,noda (node (h3 ,h4) , anaphoric) ) (5) noda (wa(monday,node (h3 ,h4) ) , anaphoric) (6) noda(node (wa(monday,h2) ,h4) ), anaphoric) (7) noda (node (h3, wa (monday ,h2) ) ), anaphoric)</Paragraph>
  </Section>
  <Section position="4" start_page="789" end_page="789" type="metho">
    <SectionTitle>
3 Theoretical Framework:
DRT and LUD
</SectionTitle>
    <Paragraph position="0"> Since the Verbmobil domain is spoken dialogues rather than isolated sentences, it is natural to choose a variant of Discourse Representation Theory, DRT (Kamp and Reyle, 1993), as the framework of its semantic formalism. To treat scope ambiguities and other underspecification phenomena adequately, we have, however, needed to extend the formalism to one which suits for representing underspecified structures (Bos, 1995). As further described in (Bos et al., 1996), LUD is a declarative description language for underspeeifled DRSs. The basic idea is that natural language expressions are not directly translated into DRSs, but into a representation that describes a number of DRSs. It is different from UDRS (Reyle, 1993) in that not only DRSs, but all predicates and discourse markers are labeled. Moreover, holes for scope domains are discerned from other labels.</Paragraph>
    <Paragraph position="1"> A LUD-representation U is a triple U =&lt; Hu, Lu, Cv &gt;, where Hu is a set of holes (variables over labels), Lu is a set of labeled conditions, and C~r a set of constraints. Holes are special labels for the slot of an operator's scope domain. A hole will be bound by means of a plugging function to a standard label which stands for a DRS of a certain element.</Paragraph>
    <Paragraph position="2"> The set of constraints is divided into alfa conditions and leq (less-or-equal) conditions, alfa conditions define presuppositions and anaphorie relations. They stipulate relations of those DRSs which do not come into scope relations to those DRSs which do. leq conditions, on the other hand, define partial order constraints between holes and labels which give a semi-lattice structure on Hv UCcr with a hole at the top (top hole). They should be maintained in the definition of a consistent subordination relation. The latter, called a possible plugging, fully specifies 2In tl~s example, each discourse relation element is taken as a predicate with the antecedent and the conclusion part as its arguments.</Paragraph>
    <Paragraph position="3"> the relations of holes to labels by way of an injective plugging function from holes to labels, which determines which hole is instantiat'ed into by (or is bound to) which label. The interpretation of a possible plugging at the top hole is the interpretation of the matrix DRS. In this way, a LUD-representation describes a set of possible pluggings at once.</Paragraph>
    <Paragraph position="4"> There are two main exceptions to this characterization of LUD. First, modifiers share its instance with the modified DRS and show no different scopal behavior. Secondly, DRSs for discourse relations are assumed to always instantiate into the top hole. In the current version, the top hole is simply assumed to be the hole argument of the sentence mood predicate of the main clause.</Paragraph>
  </Section>
  <Section position="5" start_page="789" end_page="790" type="metho">
    <SectionTitle>
4 Representations for multiple
</SectionTitle>
    <Paragraph position="0"> discourse relations In the Verbmobil semantic construction, Japanese dialogues are analysed within the same theoretical framework and with largely identical semantic macros as German ones. In order to apply the theory and implementation of LUD to Japanese, some modifications are needed. As for discourse relations, a major source of complication comes from the assumption that predicates for discourse relations have two holes as their arguments. The first problem lies in the fact that everything that goes into a leq relation to one hole cannot be in a leq relation to the other hole of the same discourse relation predicate because of its partitioning character. Another problem is the treatment of multiple occurrences of discourse relations in a sentence. We will be concentrated on the latter problem in the following sections.</Paragraph>
    <Paragraph position="1"> For the problem of processing multiple discourse dependencies there are a few approaches (Mann et al., 1992; Kurohashi and Nagao, 1994).</Paragraph>
    <Paragraph position="2"> (Gardent, 1994) uses Tree Inserting Grammar based on the feature-based Tree Adjoining Grammar (Vijay-Shanker and Joshi, 1988) to develop a formal theory about a discourse semantic representation. This paper is distinguished from these works in two perspectives: First, it concentrates on the sentential level and offers a treatment of multiple discourse relations in terms of a formalism for underspecified structures of DRSs. Secondly, it does not concern multi-functions of one discourse relation element, but multiple occurrences of various discourse relation elements.</Paragraph>
    <Paragraph position="3"> As suggested above, discourse relation elements have the following characteristic in LUD. The two holes which are contained in each of them partition the sentence in which the element occurs into  two parts, whereas it will be subordinated to another hole by way of a leq constraint as a &amp;quot;unit&amp;quot;. This has lead to the decision that a discourse relation element should be directly subordinated to the top hole. Other labels for DRSs should be subordinated to the discourse relation element in the way in which each of them is unambiguously subordinated to one of its two holes. The first problem mentioned at the beginning of this section can be dealt with in this manner if only one discourse relation element occurs in a sentence.</Paragraph>
    <Paragraph position="4"> At least two problems remain when there are a number of discourse relation elements in a sentence. First, if we keep the solution above, discourse relation elements in the sentence are all candidates for the directly subordinated position to the top hole in a semi-lattice structure. Secondly, each discourse relation element introduces a different partition of the given sentence.</Paragraph>
    <Paragraph position="5"> For a general solution, the paper proposes a device to introduce a special kind of predicate mode which has a hole as the only argument for the bottom of a lattice structure which is built by the top hole and discourse relation elements. This enables us to keep the decision, on the one hand, that discourse relation elements are in a next-to-top position in a possible plugging and to keep DRSs for other parts of the sentence underneath the mode predicate, on the other. Every discourse relation is situated above any other scope-taking element.</Paragraph>
    <Paragraph position="6"> This proposal crucially relies on the fact that for every discourse relation element which occurs in a sentence, one of its two holes can be plugged by a DRS in a lexically determined way. Additionally, it is assumed that we have a syntactic strategy in which the topic phrase is dealt with as an adjunct modification which should be interpreted in the discourse structure with respect to the main predicate of a sentence. Therefore, what is subordinated to the hole introduced by the mode predicate amounts to the matrix clause of the given sentence. In this way, an ordinary underspecification treatment of multiple discourse relations among each other gets possible.</Paragraph>
    <Paragraph position="7"> For the sentence in Fig. 1, the LUD-representation can be implemented like in (8). Labels are represented under lud preds.</Paragraph>
    <Paragraph position="8"> lud_grouping and lud_mota show among others which labels are to be treated together to construct DRSs. Under lud_scoping, alfa and loq conditions are found. The labels 112 and 113 are presuppositions of 18 and 111. leq relations read that labels are always less or equal to labels in the given order. Fig. 2 is a graphical representation of the loq constraints of (8). Discourse relations and discourse markers are abbreviated to discrol and din, respectively.</Paragraph>
    <Paragraph position="10"> The mode predicate can be seen as a secondary sentence mood predicate. For example, it serves in a similar way to the predicate used for the introduction of a propositional complement of propositional attitude verbs. This kind of use of the mode predicate does not seem to be restricted to discourse relations. For example, multiple occurences of modal expressions show a concerted behavior as regards scopal relations as in &amp;quot;we can perhaps meet there&amp;quot;. The mode predicate is applicable when multiple occurrences of predicates in one semantic class take a scope over any other scope-taking elements together but the scope relations among each other are underspecified.</Paragraph>
  </Section>
  <Section position="6" start_page="790" end_page="792" type="metho">
    <SectionTitle>
5 Possible Resolutions
</SectionTitle>
    <Paragraph position="0"> It is sometimes possible to resolve scopal underspecifications of discourse relations on several grounds. Actually, there seems to be only one</Paragraph>
    <Paragraph position="2"> plug_into (12,h5) plug_into (13,h2) Confinement of resolution possibilities depends on various factors. One of the most important factors is lexical determination of the scope domains of the antecedent part or the conclusion part of a discourse relation. Especially when one of the two is determined as anaphoric, that is, sentence external, the scope of this discourse relation seems to be wider than the others, noda in Fig. 1 is an example for this. In the same vein, the scope of noda supercedes that of a conditional discourse relation nara in Fig. 3. The latter's scope domains of the antecedent as well as the conclusion part are sentence internal.</Paragraph>
    <Paragraph position="3"> gogo-nara yamada-ga i-ru noda afternoon-cond PN-nom be-pres aux-pres  Among discourse relations with sentence external anaphoric binding there are two types: those whose antecedent part is bound sentence externally and those whose conclusion part is bound sentence externally. Discourse relation particles like dakara (therefore) belong to the former (Fig. 4), subordinate explanation relations like noda belong to the latter.</Paragraph>
    <Paragraph position="4"> dakara getsuyoubi-de daijoubu-des-u therefore monday-oblwith okay-cop-pres (I) am therefore ready for monday  Though the semantics of so-called topic phrases marked by wa goes beyond the scope of this paper, we assume that their discourse relations belongs to those whose antecedent part and conclusion part are both plugged sentence internally. This predicts a narrower scope than that of the subordinate relation noda. This not only corresponds to the intuition in (9), but is also the case in Fig. 5. gogo-wa yamada-ga i-ru noda afternoon-top PN-nom be-pres aux-pres (as \]or) the afternoon, Yamada will be here  On the other hand, scope underspecification among discourse relations cannot be disambiguated straightforwardly if they are of the same type according to the above classification. They can all be of the type whose antecedent and conclusion part are both bound sentence internally. In this case, the resolution seems to depend on the syntactic c-command information. This explains the stipulated scope relation between the topic wa and the explanative node in (9). (In (9), the scope relation is also influenced by antecedent resolution of the temporal-local modification which is needed from the syntactic information.) The same explanation holds for the scope difference which is observable between the two sentences in Fig. 6.</Paragraph>
    <Paragraph position="5"> getsuyoubi-wa gogo-nara daijoubu-da monday-top afternoon-cond okay-coppres As \]or Monday, it is ok i\] it is in the a\[ternoon gogo-nara getsuyoubi-wa daijoubu-da aftcrnoon-cond monday-top okay-cop-prcs I\] it is in the afternoon, the Monday is okay  Discourse relations can, in contrast, all be of the type whose antecedent part or conclusion part is bound sentence externally. This can be observed in Fig. 7. Not only the syntactic modality auxiliary noda, but also the discourse particle dakara includes a part which is bound sentence externally. To the extent that the c-command relation is unclear between them, the resolution remains unclear here.</Paragraph>
  </Section>
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