For features, we make the distinction between feature types and feature values (e.g., POS is a feature type and has values such as NN and VB).
each event mention is characterized by L feature types, FT, and each feature type is represented by a finite vocabulary of feature values, f v. we can represent the observable properties of an event mention as a vector of L feature type -feature value pairs (FT 1 : , where each feature value index i ranges in the feature value space associated with a feature type.