The simultaneous optimization of multiple queries submitted to adatabase system may lead to substantial savings over the current approach ofoptimizing each query separately. Isolating common subexpressions in multiplequeries and treating their execution as a sharable resource are importantprerequisites. This chapter presents techniques for recognizing, supporting,and exploiting common subexpressions in record-oriented, relational algebra,domain relational calculus, and tuple relational calculus query representations.It also investigates preconditions that transaction management mechanisms mustsatisfy to make multiple query optimization effective.
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