Since WordNet has a much finer-grained top-level classification for nouns than for verbs, we found that grouping head nouns into classes yielded useful generalizations, but it did not do so for verbs.
we calculate head dependency in three different variants: One measure is based on PP-internal noun tokens, another variant is based on noun classes for the PPinternal noun position, and another variant is based on classes for both the PP-internal and the head noun position, as indicated in equation 8.