13. A system for identifying significant topics in a document comprising: a general purpose computer having a computer usable media; computer readable program code means embodied in said computer usable media, said program code means comprising: means for extracting from said document a complete list of simplex noun phrases and corresponding heads that represent candidate significant topics of said document; means for clustering said simplex noun phrases into groups by said heads; and means for ranking said clustered simplex noun phrases by said heads in accordance with a significance measure to identify significant topics of said document from said candidate significant topics.
16. The system according to claim 13, further comprising means for post-processing said ranked simplex noun phrases to remove near-duplicatcs of said identified significant topics.