11. The method of claim 1 , wherein each first parent query is a high quality parent query for the particular child query, and each second parent query for a particular candidate sibling query is a high quality parent query for the particular sibling query.
11. The method of claim 1 , wherein each first parent query is a high quality parent query for the particular child query, and each second parent query for a particular candidate sibling query is a high quality parent query for the particular sibling query. 12. The method of claim 11 , wherein a high quality parent query has a high inverse document frequency in a corpus of documents.