OODBMS continue to be popular in area like CAD/CAM and artificial intelligence and other applications that involve complex data structures. At present, the main effort is focused on optimization of queries addressing object oriented databases. DBMS support high performance of query processing by performing operations like calculations and I/O operations. However; the major potential of performance improvement can be achieved by special preprocessing of query before its execution. This preprocessing is referred as query optimization. The main task of query optimization in DBMS is to minimize the time of query evaluation. The importance of automatic query optimization is always more effective than optimization in programming code by programmer by making use of special algorithms and techniques. An automatic optimizer operates as a computer program in an effective way.