However, a more important result of parsing the corpus using the categorical parser is that its output can be used to define a model class (i.e., a set of PCFG rules) from which a model can be learned using EM.
our model class contains the set of rules that were proposed at least once by the categorical parser in its analysis of the training corpus; in the EM experiments described below, the rule probabilities are initialized to their frequency in the categorical parser's output.