Since the CoNLL dataset is aimed at holistic SRL across all argument types, it incorporates a much larger set of verbs and tagging scenarios; as a result, the semantic role labelling of PPs is far more heterogeneous and realistic than is the case in the treebank.
we conclude that the results of our treebank preposition SRD system are not very meaningful in terms of predicting the success of the method at identifying and semantically labelling PPs in open text.