In the next step, we plan to exploit fine-grained discourse structures, e.g., dialogue acts (Ritter et al., 2010), and propose a unified model that jointly inferring discourse roles and topics of posts in context of conversation tree structures.
due to the severe sparsity of short text posts, we modify the calculation of commonly-used topic coherence measure based on word co-occurrences in messages tagged with the same hashtag, named as hashtag-document, assuming that those messages discuss related topics 8 .