D-LTAG System: Discourse Parsing with a Lexicalized Tree-Adjoining Grammar

We present an implementation of a discourse parsing system for a lexicalized TreeAjoining Grammar for discourse, specifying the integration of sentence and discourse level processing. Our system is based on the assumption that the compositional aspects of semantics at the discourse-level parallel those at the sentence-level. This coupling is achieved by factoring away inferential semantics and anaphoric features of discourse connectives. Computationally, this parallelism is achieved because both the sentence and discourse grammar are LTAG-based and the same parser works at both levels. The approach to a LTAG for discourse has been developed by (Webber & Joshi ; Webber et al. ) (among others) in some recent papers. Our system takes a discourse as input, parses the sentences individually, extracts the basic discourse units from the sentence derivations, and reparses the discourse with reference to the discourse grammar.