17. A system, comprising: a data processing apparatus having accesses to a data store storing: a query log storing query sequences for search sessions, each query sequence being a sequence including an initial query and one or more revised queries and defining an order in which the queries were submitted for a search session; and a click log storing selection data defining actions taken responsive to search results provided for the search sessions, the search results provided in response to the queries and each search result including a corresponding resource locator that specifies the location of a corresponding resource; a computer-readable medium storing instructions executable by the data processing apparatus and upon such execution cause the data processing apparatus to perform operations comprising: selecting a candidate query in a query sequence; selecting a revised query subsequent to the candidate query in the order; determining a quality score for the revised query; determining a navigation score for the revised query; and determining that the 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 in response: identifying a navigational resource for the revised query; and associating the navigational resource with the candidate query, the association specifying the navigational resource as being relevant to the candidate query in a search operation.
17. A system, comprising: a data processing apparatus having accesses to a data store storing: a query log storing query sequences for search sessions, each query sequence being a sequence including an initial query and one or more revised queries and defining an order in which the queries were submitted for a search session; and a click log storing selection data defining actions taken responsive to search results provided for the search sessions, the search results provided in response to the queries and each search result including a corresponding resource locator that specifies the location of a corresponding resource; a computer-readable medium storing instructions executable by the data processing apparatus and upon such execution cause the data processing apparatus to perform operations comprising: selecting a candidate query in a query sequence; selecting a revised query subsequent to the candidate query in the order; determining a quality score for the revised query; determining a navigation score for the revised query; and determining that the 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 in response: identifying a navigational resource for the revised query; and associating the navigational resource with the candidate query, the association specifying the navigational resource as being relevant to the candidate query in a search operation. 18. The system of claim 17 , wherein selecting the candidate query in the query sequence comprises selecting a query that has a navigation score less than the navigation score threshold and that has a quality score less than the quality score threshold.