Converting CCGs into Typed Feature Structure Grammars

In this paper, we report on a transformation scheme that turns a Categorial Grammar (CG), more specifically, a Combinatory Categorial Grammar (CCG; see (Baldridge 2002)) into a derivation- and meaning-preserving typed feature structure (TFS) grammar. We describe the main idea which can be traced back at least to work by (Karttunen 1986), (Uszkoreit 1986), (Bouma 1988), and (Calder, Klein, & Zeevat 1988). We then show how a typed representation of complex categories can be extended by other constraints, such as modes, and indicate how the Lambda semantics of combinators is mapped into a TFS representation, using unification to perform ?-conversion and ?-reduction (Barendregt 1984). We also present first findings concerning runtime measurements, showing that the PET system, originally developed for the HPSG grammar framework, outperforms the OpenCCG parser by a factor of more than 10.