Note that more important relational features would be the subtree patterns extracted from the DT.
since this does not improve the accuracy, we speculate that complete fragments, e.g., [CAUsE [ATTRI-BUTION][ELABORATION]] are more meaningful than the partial ones, e.g., [CAUsE [ATTRIBU-TION]] and [CAUsE [ELABORATION]], which may add too much uncertainty on the signature of the relations contained in the DT.