4. The method of claim 1 wherein the step of non-local process planning for a leaf node further comprises determining a strategy for performing the remaining join operators by transmission of base relations and temporary relations among the sites by an optimization criteria using the parameters of the temporary relations estimated by local process planning and the parameters of the base relations.
4. The method of claim 1 wherein the step of non-local process planning for a leaf node further comprises determining a strategy for performing the remaining join operators by transmission of base relations and temporary relations among the sites by an optimization criteria using the parameters of the temporary relations estimated by local process planning and the parameters of the base relations. 5. The method of claim 4 wherein the optimization criteria is to minimize the total time for communications among the sites.