Unsupervised Part-of-Speech Tagging with Bilingual Graph-Based Projections


We describe a novel approach for inducing unsupervised part-of-speech taggers for languages that have no labeled training data, but have translated text in a resource-rich language. Our method does not assume any knowledge about the target language (in particular no tagging dictionary is assumed), making it applicable for a wide array of resource-poor languages. We use graph-based label propagation for cross-lingual knowledge transfer and use the projected labels as constraints in an unsupervised model. Across six European languages, our approach results in an average absolute improvement of 9.7\% over the state-of-the-art baseline, and 17.0\% over vanilla hidden Markov models induced with EM.