The keyword extraction is As discussed in:
- http://www.lucidimagination.com/search/document/d051123800ab6ce7/collocations_in_mahout#26634d6364c2c0d2 - http://www.lucidimagination.com/search/document/b8d5bb0745eef6e8/n_grams_for_terms#f16fa54417697d8e
