To strike a better balance between having a rich representation of the context and improving the learner's ability to generalize, we extract a subtree from a parse tree and use it as the value of the structured feature of an instance.
given two concepts in an instance and the associated syntactic parse tree T , we retain as our subtree the portion of T that covers (1) all the nodes lying on the shortest path between the two entities, and (2) all the immediate children of these nodes that are not the leaves of T .