We create a mapping from each word in the corpus to the relevant concepts associated with it.
the result is a map S from tokens to concepts: S : w → {c, score(c|w)} (see Figure 3), where score(c|w) denotes the association of the word w with concept c, calculated as the sum of the tF-IDF values of the word w in the sentences describing c: we treat each sentence as a document and compute tF-IDF scores for the words in it.