52. A system comprising: one or more memory devices configured store executable instructions; and one or more processors configured to execute the stored instructions to cause the system to: receive a query from a user; identify a multiple word phrase in the query; identify a phrase extension of the identified phrase, wherein the phrase extension of the identified phrase is a sequence of words that begins with the identified phrase but is longer than the identified phrase, and wherein the identified phrase predicts the phrase extension based on a measure of an actual co-occurrence rate of the phrase extension and the identified phrase exceeding an expected co-occurrence rate of the phrase extension and the identified phrase in the document collection; and suggest the phrase extension to the user to use in the query.
52. A system comprising: one or more memory devices configured store executable instructions; and one or more processors configured to execute the stored instructions to cause the system to: receive a query from a user; identify a multiple word phrase in the query; identify a phrase extension of the identified phrase, wherein the phrase extension of the identified phrase is a sequence of words that begins with the identified phrase but is longer than the identified phrase, and wherein the identified phrase predicts the phrase extension based on a measure of an actual co-occurrence rate of the phrase extension and the identified phrase exceeding an expected co-occurrence rate of the phrase extension and the identified phrase in the document collection; and suggest the phrase extension to the user to use in the query. 56. The system of claim 52 , wherein the one or more processors are further configured to execute the stored instructions to cause the system to select documents from the document collection containing the phrase extension.