Patent ID: 8171029

Claim:
A method comprising: accessing an inverted index stored in a tangible storage medium, the inverted index comprising a plurality of inverted index lists for a plurality of words of a language, an inverted index list corresponding to a word indicating one or more pages that include the word, each of the plurality of inverted index lists stored by representing the inverted index list by a Boolean function and generating a binary decision diagram corresponding to the Boolean function; for each word pair of the plurality of words, the word pair comprising a first word and a second word: searching a first inverted index list and a second inverted index list, the first inverted index list corresponding to the first word, the second inverted index list corresponding to the second word; calculating an affinity between the first word and the second word according to the first inverted index list and the second inverted index list, the affinity describing a quantitative relationship between the first word and the second word; and recording the affinity in an affinity matrix; and reporting the affinity matrix.