24. 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 candidate refinement queries, Wherein selecting one or more candidate refinement queries comprises: 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 refinement query comprises adjusting the respective first score for the candidate refinement query based on a number of categories shared between the particular 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.
24. 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 candidate refinement queries, Wherein selecting one or more candidate refinement queries comprises: 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 refinement query comprises adjusting the respective first score for the candidate refinement query based on a number of categories shared between the particular 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. 31. The system of claim 24 , wherein selecting one or more candidate refinement queries comprises: 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.