nTo evaluate the resource consumption of these two strategies, we use a very simple cost model.

nWe assume that:

q a tuple access, denoted by tupacc, is 1 unit

qa tuple transfer, denoted tuptrans, is 10 units.

qrelations EMP have 1000 tuples and ASG have 400

qthere are 20 managers in relation ASG.

qdata is uniformly distributed among sites.

qrelations ASG and EMP are locally clustered on attributes RESP and ENO, respectively.

nTherefore, there is direct access to tuples of ASG (respectively, EMP) based on the value of attribute RESP (respectively, ENO).

Site 5 result=EMP U EMP 2 EMP EMP2 Site 3 Site 4 EMP1 = EMP1 Keno ASG = EMP = EMP2 DENO ASG = ASG ASG Site 1 Site 2 ASG = ORESP="Manager" ASG1 ASG = RESP="Manager" ASG2 Site 5 result=(EMP 1 U EMP2) Deno (ORESP="Manager" (ASG1 U ASG2)) ASG1 ASG2 EMP 1 EMP2 Site 1 Site 2 Site 3 Site 4