10. The computer-readable medium of claim 9 in which calculating a tf-idf value of each extracted constituent term further comprises: calculating an inverse document frequency (idf) value of the constituent term in relation to the corpus of documents; calculating a term frequency (tf) value of the constituent term; and determining the tf-idf value of the extracted constituent term based on the idf value of the constituent term and the tf value of the constituent term.
10. The computer-readable medium of claim 9 in which calculating a tf-idf value of each extracted constituent term further comprises: calculating an inverse document frequency (idf) value of the constituent term in relation to the corpus of documents; calculating a term frequency (tf) value of the constituent term; and determining the tf-idf value of the extracted constituent term based on the idf value of the constituent term and the tf value of the constituent term. 11. The computer-readable medium of claim 10 in which calculating the idf value of the constituent term further comprises calculating an idf quotient, the calculating including dividing a total number of documents in the corpus by a number of documents in which the constituent term appears.