1. A method for providing query suggestions for a user comprising: receiving a query; based on the user query, generating by at least one computer processor, from analysis of a query log of user query sessions on a publication system wherein the user query sessions comprise a plurality of high frequency queries and low frequency queries, query transitions and purchase-related events, a set of transition scores comprising transition scores for ordered pairs of the plurality of high frequency queries and low frequency queries based on transition from a query of an ordered pair of queries to a purchase-related event of the ordered pair of queries; building a set of query suggestions from the transition scores by a score accumulation process; determining whether the transition score for at least one member of the set of high frequency query suggestions meets a predetermined confidence threshold; and providing to a client machine, in response to the received user query, a list of high frequency query suggestions that have transition scores that meet the predetermined confidence threshold; generating, from the analysis, similarity metrics for suggestions for low frequency queries; determining whether the similarity metric for a suggestion for a low frequency query meets a predetermined similarity metric; and providing to a client machine, in response to the received user query, a list of low frequency query suggestions having similarity metrics that meet the predetermined similarity metric but do not meet the predetermined confidence threshold.