  Sponsored search becomes an easy platform to match potential consumers'
intent with merchants' advertising. Advertisers express their willingness to
pay for each keyword in terms of bids to the search engine. When a user's query
matches the keyword, the search engine evaluates the bids and allocates slots
to the advertisers that are displayed along side the unpaid algorithmic search
results. The advertiser only pays the search engine when its ad is clicked by
the user and the price-per-click is determined by the bids of other competing
advertisers.
