36. A system comprising: a machine-readable storage device including a program product; and one or more processors operable to execute the program product and perform operations comprising: obtaining a search query; selecting one or more previously submitted queries as candidate refinement queries, wherein the selected previously submitted queries were submitted by a user during a first search session following submission of the search query, and wherein the first search session includes search queries submitted by the user during a first period of time; selecting one or more terms from training data as candidate refinement queries, wherein a respective right context of each of the selected terms in the training data includes at least one word in a right context of the search query, and wherein a respective left context of each of the selected terms in the training data includes at least one word in a left context of the search query; determining one or more categories for the search query; determining one or more categories for each of the candidate refinement queries; determining a respective first score for each of the candidate refinement queries, wherein determining the respective first score for the candidate refinement query comprises adjusting the respective first score for the candidate refinement queries based on a number of categories shared between the candidate refinement query and the search query; and identifying as query refinements for the search query one or more of the candidate refinement queries based on the first scores.
36. A system comprising: a machine-readable storage device including a program product; and one or more processors operable to execute the program product and perform operations comprising: obtaining a search query; selecting one or more previously submitted queries as candidate refinement queries, wherein the selected previously submitted queries were submitted by a user during a first search session following submission of the search query, and wherein the first search session includes search queries submitted by the user during a first period of time; selecting one or more terms from training data as candidate refinement queries, wherein a respective right context of each of the selected terms in the training data includes at least one word in a right context of the search query, and wherein a respective left context of each of the selected terms in the training data includes at least one word in a left context of the search query; determining one or more categories for the search query; determining one or more categories for each of the candidate refinement queries; determining a respective first score for each of the candidate refinement queries, wherein determining the respective first score for the candidate refinement query comprises adjusting the respective first score for the candidate refinement queries based on a number of categories shared between the candidate refinement query and the search query; and identifying as query refinements for the search query one or more of the candidate refinement queries based on the first scores. 42. The system of claim 36 , the operations further comprising: selecting as candidate refinement queries one or more sibling queries of the search query, wherein sibling queries are queries that have one or more shared parent queries in common, and wherein each of the sibling queries was submitted during a second search session following submission of a shared parent query during the first search session.