tailieunhanh - Báo cáo khoa học: "Discourse Relations: A Structural and Presuppositional Account Using Lexicalised TAG*"

We show that discourse structure need not bear the full burden of conveying discourse relations by showing that many of them can be explained nonstructurally in terms of the grounding of anaphoric presuppositions (Van der Sandt, 1992). This simplifies discourse structure, while still allowing the realisation of a full range of discourse relations. This is achieved using the same semantic machinery used in deriving clause-level semantics. | Discourse Relations A Structural and Presuppositional Account Using Lexicalised TAG Bonnie Webber Univ of Edinburgh bonnie@ Alistair Knott Univ of Otago alik@ Matthew Stone Rutgers Univ mdstone @ cs .rut gers. edu Aravind Joshi Univ of Pennsylvania joshi@ Abstract We show that discourse structure need not bear the full burden of conveying discourse relations by showing that many of them can be explained non-structurally in terms of the grounding of anaphoric presuppositions Van der Sandt 1992 . This simplifies discourse structure while still allowing the realisation of a full range of discourse relations. This is achieved using the same semantic machinery used in deriving clause-level semantics. 1 Introduction Research on discourse structure has by and large attempted to associate all meaningful relations between propositions with structural connections between discourse clauses syntactic clauses or structures composed of them . Recognising that this could mean multiple structural connections between clauses Rhetorical Structure Theory Mann and Thompson 1988 simply stipulates that only a single relation may hold. Moore and Pollack 1992 argue that both informational semantic and intentional relations can hold between clauses simultaneously and independently. This suggests that factoring the two kinds of relations might lead to a pair of structures each still with no more than a single structural connection between any two clauses. But examples of multiple semantic relations are easy to find Webber et al. 1999 . Having structure account for all of them leads to the complexities shown in Figure 1 including the crossing dependencies shown in Fig. 1c. These structures are no longer trees making it difficult to define a compositional semantics. This problem would not arise if one recognised additional non-structural means of conveying semantic relations between propositions and modal Our thanks to Mark Steedman Katja Markert Gann .