After examining the statistics of relative clauses in Stanford dependencies of the training set, we found that when the subject is present in the relative clause while the object is missing, the relative clause is most likely to be an object relative clause; when the subject is missing but the object is present, it is most likely to be a subject relative clause; and if both subject and object are absent, it is most likely to be a subject relative clause.
we labeled an 'of-asso' dependency between the extracted topic and the subject of the relative clause.