Genre distinctions for discourse in the Penn TreeBank

Proceedings of the 47th Annual Meeting of the ACL and the 4th IJCNLP of the AFNLP, pages 674–682, Suntec, Singapore, 2-7 August 2009. c⃝2009 ACL and AFNLP Genre distinctions for Discourse in the Penn TreeBank Bonnie Webber School of Informatics University of Edinburgh Edinburgh EH8 9LW, UK bonnie.webber@ed.ac.uk Abstract Articles in the Penn TreeBank were iden- tified as being reviews, summaries, let- ters to the editor, news reportage, correc- tions, wit and short verse, or quarterly profit reports. All but the latter three were then characterised in terms of fea- tures manually annotated in the Penn Dis- course TreeBank — discourse connectives and their senses. Summaries turned out to display very different discourse features than the other three genres. Letters also appeared to have some different features. The two main findings involve (1) differ- ences between genres in the senses asso- ciated with intra-sentential discourse con- nectives, inter-sentential discourse con- nectives and inter-sentential discourse re- lations that are not lexically marked; and (2) differences within all four genres be- tween the senses of discourse relations not lexically marked and those that are marked. The first finding means that genre should be made a factor in automated sense labelling of non-lexically marked discourse relations. The second means that lexically marked relations provide a poor model for automated sense labelling of relations that are not lexically marked. 1 Introduction It is well-known that texts differ from each other in a variety of ways, including their topic, the read- ing level of their intended audience, and their in- tended purpose (eg, to instruct, to inform, to ex- press an opinion, to summarize, to take issue with or disagree, to correct, to entertain, etc.). This paper considers differences in texts in the well- known Penn TreeBank (hereafter, PTB) and in particular, how these differences show up in the Penn Discourse TreeBank (Prasad et al., 2008). It first describes ways in which texts can vary (Section 2). It then illustrates the variety of texts to be found in the the PTB and suggests their grouping into four broad genres (Section 3). After a brief introduction to the Penn Discourse Tree- Bank (hereafter, PDTB) in Section 4, Sections 5 and 6 show that these four genres display differ- ences in connective frequency and in terms of the senses associated with intra-sentential connectives (eg, subordinating conjunctions), inter-sentential connectives (eg, inter-sentential coordinating con- junctions) and those inter-sentential relations that are not lexically marked. Section 7 considers re- cent efforts to induce effective procedures for au- tomated sense labelling of discourse relations that are not lexically marked (Elwell and Baldridge, 2008; Marcu and Echihabi, 2002; Pitler et al., 2009; Wellner and Pustejovsky, 2007; Wellner, 2008). It makes two points. First, because gen- res differ from each other in the senses associated with such relations, genre should be made a factor in their automated sense labelling. Secondly, be- cause different senses are being conveyed when a relation is lexically marked than when it isn’t, lex- ically marked relations provide a …

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