19. The system of claim 17 , wherein the candidate query is further selected in response to determining that a quality score for the revised query is greater than a quality score threshold and that the navigation score for the revised query is greater than a navigation score threshold, and selecting the candidate query comprises: selecting a query that is prior to the revised query in the query sequence; determining a quality score for the selected query; determining navigation score for the selected query; and determining that the selected query is a candidate query if the quality score of the selected query is less than the quality score threshold and the navigation score of the selected query is less than the navigation score threshold.
19. The system of claim 17 , wherein the candidate query is further selected in response to determining that a quality score for the revised query is greater than a quality score threshold and that the navigation score for the revised query is greater than a navigation score threshold, and selecting the candidate query comprises: selecting a query that is prior to the revised query in the query sequence; determining a quality score for the selected query; determining navigation score for the selected query; and determining that the selected query is a candidate query if the quality score of the selected query is less than the quality score threshold and the navigation score of the selected query is less than the navigation score threshold. 20. The system of claim 19 , wherein selecting the candidate query further comprises determining the selected query is a candidate query only if the probability of revision from the candidate query to the revised query to is greater than a probability threshold that is greater than the probability of entry of the revised query.