For convenience we assume that r i = {δ} for i < 1 ∨ i > n. Definition 1 can be easily modified to take those constraints into account.
the model assigns probability 0 to all label sequences which are inconsistent with the constraints imposed by r: The normalization factor within the constrained context is defined as We describe here two methods of inference using CCRFs: finding the most probable label sequence given the sentence and assigning marginal probabilities to individual labels from restricted sets.