tailieunhanh - Báo cáo khoa học: "TENSE TREES AS THE "FINE STRUCTURE" OF DISCOURSE"

We present a new compositional tense-aspect deindexing mechanism that makes use of tense trees as components of discourse contexts. The mechanism allows reference episodes to be correctly identified even for embedded clauses and for discourse that involves shifts in temporal perspective, and permits deindexed logical forms to be automatically computed with a small number of deindexing rules. | TENSE TREES AS THE FINE STRUCTURE OF DISCOURSE Chung Hee Hwang Lenhart K. Schubert Department of Computer Science University of Rochester Rochester New York 14627 u. s. A. hwang Schubert ABSTRACT We present a new compositional tense-aspect deindexing mechanism that makes use of tense trees as components of discourse contexts. The mechanism allows reference episodes to be correctly identified even for embedded clauses and for discourse that involves shifts in temporal perspective and permits deindexed logical forms to be automatically computed with a small number of deindexing rules. 1 Introduction Work on discourse structure . Reichman 1985 Grosz and Sidner 1986 Allen 1987 has so far taken a rather coarse high-level view of discourse mostly treating sentences or sentence-like entities utterance units contributions etc. as the lowest-level discourse elements. To the extent that sentences are analyzed at all they are simply viewed as carriers of certain features relevant to supra-sentential discourse structure cue words tense time adverbials aspectual class into-national cues and others. These features are presumed to be extractable in some straightforward fashion and provide the inputs to a higher-level discourse segment analyzer. However sentences or their logical forms are not in general flat with a single level of structure and features but may contain multiple levels of clausal and adverbial embedding. This substructure can give rise to arbitrarily complex relations among the contributions made by the parts such as temporal and discourse relations among subordinate clausal constituents and events or states of affairs they evoke. It is therefore essential in a comprehensive analysis of discourse structure that these intra-sentential relations be systematically brought to light and integrated with larger-scale discourse structures. Our particular interest is in tense aspect and other indicators of temporal structure. We are developing a uniform

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