Several other variants of CRF model has been proposed in the machine learning literature, such as the generalized expectation method (Mann and McCallum, 2008), which introduce knowledge by incorporating a manually annotated feature distribution into the regularizer, and the JESS-CM (Suzuki and Isozaki, 2008), which use a EM-like method to iteratively optimize the parameter on both the annotated data and unlabeled data.
we directly incorporate the likelihood of partial annotation into the objective function.