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 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; and responsive to said determining, adding the natural language sentence to the test set, by executing seventh instructions in the computer system.