BCNF and Dependency Preservation Constraints,including functional dependencies,are costly to check in practice unless they pertain to only one relation If it is sufficient to test only those dependencies on each individual relation of a decomposition in order to ensure that al/functional dependencies hold,then that decomposition is dependency preserving. Because it is not always possible to achieve both BCNF and dependency preservation,we consider a weaker normal form,known as third normal form. Database System Concepts-5th Edition,Oct 5,2006 7.19 @Silberschatz,Korth and SudarshanDatabase System Concepts - 5 7.19 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 BCNF and Dependency Preservation Constraints, including functional dependencies, are costly to check in practice unless they pertain to only one relation If it is sufficient to test only those dependencies on each individual relation of a decomposition in order to ensure that all functional dependencies hold, then that decomposition is dependency preserving. Because it is not always possible to achieve both BCNF and dependency preservation, we consider a weaker normal form, known as third normal form