Annotations of the Discourse Relations. ARG1AND ARG2 There are two kinds of realization of the discourse relations in the PDTB. The first type is realized by explicit connectives which are lexically identifiable (Xxxxxx, Xxxxx, Xxxxxxxxxx, Xxxxxx, Xxxxxx, Xxx, et al., 2006; Xxxxxx, et al., 2008a). Explicit connectives are classified into three syntactical classes: subordinating conjunctions (e.g., when, because, although, so that, if, etc.), coordinating conjunctions (e.g., and, but, or, etc.), and discourse adverbials (e.g., however, for example, then, otherwise, etc.). All explicit connectives bound two arguments which are labeled as Arg1 and Arg2. There is no limitation for the location and span length of the Arg1 and Arg2, and thus, they can be anywhere in the text and they can be single or multiple sentences or clauses. Identifying the Arg2 is relatively easier than identifying Arg1 because Arg2 is mostly adjacent to the discourse connective. Additionally, annotation of the arguments is restricted bys the Minimality principle. The Minimality principle imposes the annotation to be as short as possible to define the discourse relation adequately. The second type of discourse relations is realized by implicit connectives. Implicit connectives are not identifiable by an overt lexical item such as a discourse connective. These relations are inferred relations between adjacent sentences. The annotation of implicit connectives is performed by selecting the explicit connective that best illuminates the discourse relation. The TDB project group did not annotate implicit relations.
