20. The method of claim 19 further comprising: utilizing one of a parse-tree based approach or a chunking-based approach to extract phrases used by the first user in a constraint specification and form a pool of examples of how to lexicalize constraints in the user input; and generalizing the constraints into phrase patterns by replacing constraints with corresponding semantic class names.
22. The method of claim 20 wherein the chunking-based approach tags all user utterances using a part-of-speech tagger, and parsed by one of a shallow parser or deep structure parser.