4. The method of claim 1 , wherein calculating the similarity scores for the at least the portion of the first queries relative to the plurality of head queries further comprises: calculating first scores according to the response similarity between user selections of the search results for the at least the portion of the first queries and user selections of the search results for the plurality of head queries; calculating second scores according to co-occurrences of the at least the portion of the first queries with the plurality of head queries in a same user session; calculating third scores according to textual similarity of the at least the portion of the first queries to the plurality of head queries; and calculating the similarity scores for the at least the portion of the first queries according to a combination of the first, second, and third scores.
1. A method for searching, the method comprising: receiving, by a computer system, first queries, from a user; selecting, by the computer system, a plurality of head queries from among the first queries; clustering, by the computer system, the first queries, exclusive of the plurality of head queries, to the plurality of head queries by: calculating similarity scores for at least a portion of the first queries relative to the plurality of head queries; and clustering the at least the portion of the first queries to the plurality of head queries according to the similarity scores; associating, by the computer system, one or more categories with each head query of the plurality of head queries; receiving, by the computer system, a second query; determining a similarity between the second query and at least one of a selected head query of the plurality of head queries; associating, by the computer system, the second query with the selected head query of the plurality of head queries according to the similarity between the second query and the at least one of the selected head query; and identifying, by the computer system, one or more documents relevant to the second query using the one or more categories associated with the selected head query of the plurality of head queries; wherein: calculating the similarity scores for the at least the portion of the first queries relative to the plurality of head queries further comprises: evaluating response similarity between user selections of search results for the at least the portion of the first queries and user selections of search results for the plurality of head queries by evaluating an equation: Sim ( q 1 , q 2 ) = P 1 · P 2  P 1  2 ⁢  P 2  2 where Sim (q 1 ,q 2 ) is a similarity score of a first query a 1 of the at least the portion of the first queries, q 2 is a head query of the plurality of head queries, P 1 is a vector of user selection counts for search results of q 1 , and P 2 is a vector of user selection counts for search results of q 2 .