A Gibbs Sampler for Phrasal Synchronous Grammar Induction
Phil Blunsom, Trevor Cohn, Chris Dyer and Miles Osborne
In: 47th Annual Meeting of the ACL and the 4th IJCNLP of the AFNLP, 2-7 August 2009, Singapore.
We present a phrasal synchronous grammar model of translational equivalence. Unlike previous approaches, we do not resort to heuristics or constraints from a word-alignment model, but instead directly induce a synchronous grammar from parallel sentence-aligned corpora. We use a hierarchical Bayesian prior to bias towards compact grammars with small translation units. Inference is per- formed using a novel Gibbs sampler over synchronous derivations. This sampler side-steps the intractability issues of previous models which required inference over derivation forests. Instead each sampling iteration is highly efficient, allowing the model to be applied to larger transla- tion corpora than previous approaches.