The Overall Markedness of Discourse Relations

Proceedings of the 2015 Conference on Empirical Methods in Natural Language Processing, pages 1114–1119, Lisbon, Portugal, 17-21 September 2015. c⃝2015 Association for Computational Linguistics. The Overall Markedness of Discourse Relations Lifeng Jin and Marie-Catherine de Marneffe Department of Linguistics The Ohio State University {jin, mcdm}@ling.osu.edu Abstract Discourse relations can be categorized as continuous or discontinuous in the hypoth- esis of continuity (Murray, 1997), with continuous relations expressing normal succession of events in discourse such as temporal, spatial or causal. Asr and Dem- berg (2013) propose a markedness mea- sure to test the prediction that discontin- uous relations may have more unambigu- ous connectives, but restrict the marked- ness calculation to relations with explicit connectives only. This paper extends their measure to explicit and implicit relations and shows that results from this extension better fit the continuity hypothesis predic- tions both for the English Penn Discourse (Prasad et al., 2008) and the Chinese Dis- course (Zhou and Xue, 2015) Treebanks. 1 Introduction Discourse relations between units of text are cru- cial for the production and understanding of dis- course. Different taxonomies of discourse rela- tions have been proposed (i.a. Hobbs (1985), Las- carides and Asher (1993) and Knott and Sanders (1998)). One taxonomy is based on deictic conti- nuity (Segal et al., 1991; Murray, 1997): continu- ity in the sense of Segal et al. (1991) means that the same frame of reference is maintained, for ex- ample by subsequent sentences talking about the same event, without a shift in perspective (Asr and Demberg, 2012). For instance, a causal relation such as I was tired, so I drank a cup of coffee. is continuous, and adversatives show discontinuous relations: I drank a cup of coffee but I was still tired. Other continuous relations include temporal succession, topic succession and so on. The conti- nuity hypothesis predicts that sentences connected by continuous relations are easier to understand than ones connected by discontinuous relations. Previous work on continuity hypothesis (Maury and Teisserenc, 2005; Cain and Nash, 2011; Hoek and Zufferey, 2015) suggests that discourse connectives are indicators of the continuity of discourse and help the interlocutors predict the level of continuity of upcoming sentences. Se- gal et al. (1991) propose that connectives which signal discontinuous discourse relations, such as but, are the marked ones because they indicate harder-to-comprehend content. Asr and Demberg (2012, 2013) extend this idea to discourse rela- tions, proposing that discourse relations which are discontinuous, or posing a conceptual difficulty (Haspelmath, 2006), may be less explicitly con- veyed in text, or more explicitly marked by a con- nective which unambiguously conveys that spe- cific relation than continuous ones. They propose a new measure called markedness to capture this, but when computed on the Penn Discourse Tree- bank, results do not fit the continuity theory well. This paper improves on Asr and Demberg (2013)’s measure and shows that the results on the Penn Discourse and the Chinese Discourse Treebanks fit the continuity hypothesis very well. 2 Discourse Treebanks Penn Discourse Treebank The …

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