Unlike in an entity-mention model, however, in a cluster ranker, (1) a training instance is created between each discourse-old mention m k and each of its preceding clusters; and (2) since we are training a model for ranking clusters, the assignment of class values to training instances is similar to that of a mention ranker.
the class value of a training instance i(c j , m k ) created for m k is the rank of c j among the competing clusters, which is 2 if m k belongs to c j , and 1 otherwise.