Explicit and Implicit Discourse Relations in the Prague Discourse Treebank

Coherence of a text is provided by various language means, including discourse connectives (coordinating and subordinating conjunctions, adverbs etc.). However, semantic relations between text segments can be deduced without an explicit discourse connective, too (the so called implicit discourse relations, cf. He missed his train. 0 He had to take a taxi.). In our paper, we introduce a corpus of Czech annotated for implicit discourse relations (Enriched Discourse Annotation of Prague Discourse Treebank Subset 1.0) and we analyze some of the factors influencing the explicitness/implicitness of discourse relations, such as the text genre, semantic type of the discourse relation and the presence of negation in discourse arguments.