Mapping Explicit and Implicit Discourse Relations between the RST - DT and the PDTB 3.0 (2023)

Abstract: In this paper we propose a first empirical mapping between the RST-DT and the PDTB 3.0. We provide an original algorithm which allowed the mapping of 6,510 (80.0%) explicit and implicit discourse relations between the overlapping articles of the RST-DT and PDTB 3.0 discourse annotated corpora. Results of the mapping show that while it is easier to align segments of implicit discourse relations, the mapping obtained between the aligned explicit discourse relations is more unambiguous.

## introduction different linguistic frameworks have been proposed to model the discourse relations that hold between textual segments. two widely used frameworks are the rhetorical structure theory (rst) @xcite and the penn discourse treebank (pdtb) @xcite . following these frameworks, several annotated corpora have been developed for a wide variety of nlp tasks, such as discourse parsing @xcite , implicit discourse relation classification @xcite and discourse generation @xcite . since generating and manually annotating discourse corpora at the large scale required for finetuning large language models is prohibitively expensive and laborious, a viable alternative is to establish a mapping between already existing corpora so that they can be used seamlessly and interchangeably together. the two primary discourse annotated corpora are the rst-dt @xcite and the pdtb (pdtb 1.0, 2.0 and 3.0) @xcite @xcite . however, since both corpora are annotated based on different frameworks, they differ in how they segment and label discourse relations. the resulting structural differences limit the extent to which they can be used together to train discourse models. in this paper, we present a first empirical mapping between the rst-dt and the pdtb 3.0 based on the overlapping sections of the two annotated corpora. previous work has addressed such a mapping between the rst-dt and pdtb 2.0 @xcite proposed a theoretical mapping between both frameworks, while @xcite established an empirical mapping based on the subset of the corpora that they share. however, to the best of our knowledge, no work has proposed a mapping between the rst-dt and the pdtb 3.0. ## background the linguistic frameworks behind the rst-dt and the pdtb differ in how textual units are segmented and in how discourse relations are defined. ## previous work previous work has attempted to establish a mapping between the rst-dt and the pdtb corpora. most recently, @xcite proposed an empirical mapping between the rst-dt and the pdtb 2.0. their approach was able to map 76% of the pdtb explicit and implicit discourse relations (senses) to an rst-dt relation based on an analysis of the overlapping sections of the two corpora. additionaly, @xcite compare the results of their empirical mapping with the theoretically mappings proposed by @xcite , @xcite and @xcite . they found that their empirical results matched the theoretical mappings in more than 70% of the explicit relations, but only in less than 50% of the implicit relations. another empirical mapping between the rst-dt and the pdtb 2.0 corpora was conducted by @xcite . they focused only on implicit discourse relations where an exact segment span matching was possible, which included a total of 472 discourse relations. however, previous work was based exclusively on the pdtb 2.0 corpus. given the significant changes in the pdtb 3.0, it has become necessary to develop a new mapping algorithm to accommodate the new annotation guidelines and establish a first empirical mapping between the rst-dt and the pdtb 3.0. ## corpora the rst-dt corpus @xcite consists of 385 wall street journal articles annotated with 20,017 discourse relations, while the pdtb foot_2 corpus @xcite consists of 2162 wall street journal articles with 53,631 discourse relation annotations. both corpora overlap on 365 articles, allowing us to establish a direct mapping between the two. ## aligning and mapping relations similarly to @xcite , and given the smaller number of pdtb relations compared to rst-dt relations (see ## results we first present the results of the relation alignment (see section 5.1) and then present the relation mapping results (see section 5.2). ## conclusion in this paper we have presented a first empirical mapping between the rst-dt and the pdtb 3.0 annotated corpora. following our proposed algorithms we were able to map 6,510 (80.0%) of the explicit and implicit discourse relations in the 365 wall street journal articles overlapping the rst-dt and the pdtb 3.0 corpora. compared to the 76% successfully mapped relations obtained by @xcite in their empirical mapping between the rst-dt and the pdtb 2.0, we were able to achieve a 4% improvement in mapping coverage. our alignment results show a clearer correspondence between segments of implicit discourse relations when compared to segments of explicit relations. this is a consequence of the difference in annotation between the two corpora. since the rst-dt establishes discourse relations between all adjacent text segments, the pdtb often establishes explicit relations between text segments which are not adjacent. this creates a challenge for the alignment algorithm. however, when an alignment was found, we observed a clearer mapping between explicit discourse relations than between implicit discourse relations. this stems from the presence of discourse connectives which allow for a more objective interpretation of the relations.