1. A computer-implemented method, comprising: associating each of a plurality of parent queries with a respective group of one or more child queries for the parent query, wherein each child query was submitted during a respective session following submission of its associated parent query during the session; identifying one or more candidate sibling queries for a particular child query, wherein the particular child query is a child query for one or more first parent queries in the plurality of parent queries and each candidate sibling query for the particular child query is a child query for one or more second parent queries in the plurality of queries, wherein for each candidate sibling query, the one or more second parent queries for the candidate sibling query and the one or more first parent queries have a group of shared parent queries in common and the group of shared parent queries has a size that satisfies a common-query threshold; and selecting one or more final sibling queries for the particular child query from the one or more candidate sibling queries, and associating the final sibling queries with the particular child query as query refinements for the particular child query.