2. The method of claim 1 , wherein computing a score for the second term comprises: computing respective changes in co-occurrence frequency between corresponding elements of the first vector and the second vector; generating an order of co-occurring terms according to the corresponding computed changes in co-occurrence frequency; and computing a measure of importance of a top number of co-occurring terms in the order.
6. The method of claim 2 , wherein the measure of importance for a term x is based on frequencies of terms that co-occur with the term in received search queries, and is given by: imp ⁡ ( x ) = 1 - ∑ i = 1 k ⁢ H i · DF ⁡ ( Term i ) , wherein H i is a co-occurrence frequency value for Term i and DF(Term i ) is a document frequency value of Term i .