Database queries havebecome increasingly complex in the age of the distributed DBMS (DDBMS). Thisposes a difficulty for the programmer but also for the DDBMS. Queryoptimization is a difficult enough task in a non-distributed environment.Anyone who has tried to study and understand a cost-based query optimizer for arelational DBMS (such as DB2 or Sybase SQL Server) can readily attest to thisfact. When adding distributed data into the mix, query optimization becomeseven more complicated. This paper focuses query optimization in distributedRDBMS.