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.
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. 18. The system according to claim 13, wherein said significance measure is based at least in part on a frequency of said heads in said simplex noun phrases.