Basic Steps in Query Processing Optimization A relational algebra expression may have many equivalent expressions E.g.,balance<2500(Ibalance(account))is equivalent to Ibalance(balance<2500(account)) Each relational algebra operation can be evaluated using one of several different algorithms Correspondingly,a relational-algebra expression can be evaluated in many ways. Annotated expression specifying detailed evaluation strategy is called an evaluation-plan. E.g.,can use an index on balance to find accounts with balance 2500, or can perform complete relation scan and discard accounts with balance≥2500 Database System Concepts-5th Edition,Aug 27,2005. 13.5 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 13.5 ©Silberschatz, Korth and Sudarshan th Edition, Aug 27, 2005. Basic Steps in Query Processing : Optimization A relational algebra expression may have many equivalent expressions E.g., balance2500(balance(account)) is equivalent to balance(balance2500(account)) Each relational algebra operation can be evaluated using one of several different algorithms Correspondingly, a relational-algebra expression can be evaluated in many ways. Annotated expression specifying detailed evaluation strategy is called an evaluation-plan. E.g., can use an index on balance to find accounts with balance < 2500, or can perform complete relation scan and discard accounts with balance  2500