8. A computer system comprising: one or more processors which process program instructions; a memory device connected to said one or more processors; and program instructions residing in said memory device for syntactically classifying a natural language sentence by receiving the natural language sentence, parsing the natural language sentence to derive a parse tree having a plurality of nodes, identifying a particular one of the nodes that corresponds to an element of interest in the natural language sentence, extracting syntactic information from the parse tree relative to the particular node corresponding to the element of interest, recording the syntactic information as a classification for the natural language sentence, determining that the classification for the natural language sentence is different from classifications of other natural language sentences in a test set according to at least one predetermined similarity criterion related to the syntactic information wherein the predetermined similarity criterion allows two given sentences to be deemed similar even when the two given sentences have different classifications, and responsively adding the natural language sentence to the test set.
13. The computer system of claim 8 wherein the particular node corresponding to the element of interest is identified by scanning the parse-tree for the element in a top-down, left-to-right, depth-first order.