Inducing Compact but Accurate Tree-Substitution Grammars
Trevor Cohn, Phil Blunsom and Sharon Goldwater
In: NAACL 2009, 31 May - 5 June 2009, Boulder, USA.
Tree substitution grammars (TSGs) are a compelling alternative to context-free grammars for modelling syntax. However, many popular techniques for estimating weighted TSGs (under the moniker of Data Oriented Parsing) suffer from the problems of inconsistency and over-fitting. We present a theoretically principled model which solves these problems us- ing a Bayesian non-parametric formulation. Our model learns compact and simple gram- mars, uncovering latent linguistic structures (e.g., verb subcategorisation), and in doing so far out-performs a standard PCFG.