Svetlozar Nestorov Chuang Liu Ian T. Foster Efficient Processing of Relational Queries with Sum Constraints. 440-451 2007 conf/waim/2007 APWeb/WAIM http://dx.doi.org/10.1007/978-3-540-72524-4_46 db/conf/waim/waim2007.html#NestorovLF07