21. The computing device of claim 20 , wherein the processing unit is further configured to select a first tuple from the second set of tuples, wherein the first tuple locally dominates a second tuple from the second set of tuples.
21. The computing device of claim 20 , wherein the processing unit is further configured to select a first tuple from the second set of tuples, wherein the first tuple locally dominates a second tuple from the second set of tuples. 22. The computing device of claim 21 , wherein the joined relation comprises a second joined tuple which is joined based on the first tuple selected from the second set of tuples and a third tuple selected from the third set of tuples.