Introduction Alternative ways of evaluating a given query Equivalent expressions Different algorithms for each operation Π ame,title name,title dept_name Music instructor Odept_name=Music teaches course instructor teaches course Database System Concepts-6th Edition 1.3 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 6 1.3 ©Silberschatz, Korth and Sudarshan th Edition Introduction Alternative ways of evaluating a given query Equivalent expressions Different algorithms for each operation