44. 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 select documents from the document collection containing the phrase extension.
44. 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 select documents from the document collection containing the phrase extension. 50. The system of claim 44 , wherein the one or more processors are further configured to execute the stored instructions to cause the system to provide the selected documents to a user in response to the query.