θ ∈ R d and γ ∈ R d and defines a joint probability of y and z conditioned on x as follows: where Y(x, z) is the set of all possible label sequences for x and z, and HUCRF forces the interaction between the observations and the labels at each position j to go through a latent variable z j : see Figure 1 for illustration.
hUCRF with pre-training with Brown clusters (hUCRF B ) and CCA-based clusters (hUCRF C ) further improves performance to 91.36% and 91.37%, respectively.