6. The method of claim 1 , further comprising using prior knowledge about a size of a respective set, |Dj|, to further reduce communication cost, where 1≦j≦q, and where q represents all keywords in the query.
8. The method of claim 6 , further comprising sending the query first to a node ĵ=arg max{|Dj|} and then to a next node which has a second largest value for |Dj| to optimally perform an OR query.