|Katsuhiko Hayashi, Tsutomu Hirao and Masaaki Nagata|
Two heuristic rules that transform Rhetorical Structure Theory discourse trees into discourse dependency trees (DDTs) have recently been proposed (Hirao et al., 2013; Li et al., 2014), but these rules derive significantly different DDTs because their conversion schemes on multinuclear relations are not identical. This paper reveals the difference among DDT formats with respect to the following questions: (1) How complex are the formats from a dependency graph theoretic point of view? (2) Which formats are analyzed more accurately by automatic parsers? (3) Which are more suitable for text summarization task? Experimental results showed that Hirao’s conversion rule produces DDTs that are more useful for text summarization, even though it derives more complex dependency structures.