Constrained Sequence Classification for Lexical Disambiguation

Abstract. This paper addresses lexical ambiguity with focus on a par-ticular problem known as accent prediction, in that given an accentless sequence, we need to restore correct accents. This can be modelled as a sequence classification problem for which variants of Markov chains can be applied. Although the state space is large (about the vocabulary size), it is highly constrained when conditioned on the data observation. We investigate the application of several methods, including Powered Product-of-N-grams, Structured Perceptron and Conditional Random Fields (CRFs). We empirically show in the Vietnamese case that these methods are fairly robust and efficient. The second-order CRFs achieve best results with about 94 % term accuracy