10. The system recited in claim 9 , wherein the one or more processors are further operable when executing the instructions to: extract from one or more logs one or more query sequences, wherein each query sequence comprises one or more queries received at a search engine ordered according to when the one or more queries are received at the search engine; construct one or more query-suggestion pairs to be included in the set of query-suggestion pairs from each query sequence, wherein constructing one query-suggestion pair from one query sequence comprises: select from the one query sequence two queries; and construct the one query-suggestion pair with a preceding one of the two queries as the query and a succeeding one of the two queries as the suggestion.
10. The system recited in claim 9 , wherein the one or more processors are further operable when executing the instructions to: extract from one or more logs one or more query sequences, wherein each query sequence comprises one or more queries received at a search engine ordered according to when the one or more queries are received at the search engine; construct one or more query-suggestion pairs to be included in the set of query-suggestion pairs from each query sequence, wherein constructing one query-suggestion pair from one query sequence comprises: select from the one query sequence two queries; and construct the one query-suggestion pair with a preceding one of the two queries as the query and a succeeding one of the two queries as the suggestion. 11. The system recited in claim 10 , wherein: the one or more queries of each query sequence are from a same user session; and each query of each query sequence is followed by at least one click indicated in the logs.