3. The computer implemented method of claim 1 , wherein said first probability is determined based on collective occurrences of receiving said second query term subsequent to receiving said first query term in respective searching sessions of said prior searching activities with respect to said search engine, and based on a conversion rate associated with said second query term; and wherein said second probability is determined based on collective occurrences of receiving said first query term in said prior searching activities and based on a conversion rate associated with said first query term.
3. The computer implemented method of claim 1 , wherein said first probability is determined based on collective occurrences of receiving said second query term subsequent to receiving said first query term in respective searching sessions of said prior searching activities with respect to said search engine, and based on a conversion rate associated with said second query term; and wherein said second probability is determined based on collective occurrences of receiving said first query term in said prior searching activities and based on a conversion rate associated with said first query term. 4. The computer implemented method of claim 3 , wherein said prior searching activities comprises: a sequence of search query terms entered by a respective user in a respective prior searching session; a purchase action in said respective prior searching session, or a leave-without-purchase action in said respective prior searching session.