Our chosen method to enforce constraints takes into account current knowledge (i.e., initial decoding from CRF) when estimating probabilities of labels by conditioning posterior probabilities on the presence of label A and B based on current observations.
if only A missing, i.e., |t A | = 0 then we search and we define y C t = A ∀t ∈ t * A and In this method, ϕ represents the the posterior conditional probability given the observed locations of the required labels.