The Impact of Deep Hierarchical Discourse Structures in the Evaluation of Text Coherence
Previous work by Lin et al. (2011) demonstrated the effectiveness of using discourse relations for evaluating text coherence. However, their work was based on discourse relations annotated in accordance with the Penn Discourse Treebank (PDTB) (Prasad et al. 2008) which encodes only very shallow discourse structures; therefore, they cannot capture long distance discourse dependencies. In this paper, we study the impact of deep discourse structures for the task of coherence evaluation, using two approaches: (1) We compare a model with features derived from discourse relations in the style of Rhetorical Structure Theory (RST) (Mann and Thompson, 1988) which annotate the full hierarchical discourse structure, against our re implementation of Lin et al.'s model; (2) We compare a model encoded using only shallow RST style discourse relations, against the one encoded using the complete set of RST style discourse relations. With an evaluation on two tasks, we show that deep discourse structures are truly useful for better differentiation of text coherence, and in general, RST style encoding is more powerful than PDTBstyle encoding in these settings.
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