1. A method of syntactically classifying a natural language sentence comprising: receiving the natural language sentence in computer-readable form, by executing first instructions in a computer system; parsing the natural language sentence to derive a parse tree having a plurality of nodes, by executing second instructions in the computer system; identifying a particular one of the nodes that corresponds to an element of interest in the natural language sentence, by executing third instructions in the computer system; extracting syntactic information from the parse tree relative to the particular node corresponding to the element of interest, by executing fourth instructions in the computer system; recording the syntactic information as a classification for the natural language sentence, by executing fifth instructions in the computer system; 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, by executing sixth instructions in the computer system, wherein the predetermined similarity criterion allows two given sentences to be deemed similar even when the two given sentences have different classifications; and responsive to said determining, adding the natural language sentence to the test set, by executing seventh instructions in the computer system.