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BCNF - Boyce-Codd Normal Form By P.Mirunalini Asst Prof CSE...

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Boyce-Codd Normal Form By: P.Mirunalini Asst. Prof, CSE SSN College of Engineering
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Overview Dependency preservation Boyce/Codd Normal Form
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Dependency Preservation Relvar SECOND could be decomposed into: A: SC { SUPPLIER_NUMBER, CITY } CS { CITY, STATUS } • Alternative decomposition B: B: SC { SUPPLIER_NUMBER, CITY } SS { SUPPLIER_NUMBER, STATUS } • The Decomposition A and B is nonloss and the projections are in 3NF Decomposition B is less satisfactory than A.
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Dependency Preservation In decomposition A, the two projections are independent of one another Updates can be made to either one without regard for the other. Not violates the primary key uniqueness Join of the projections will always produces the original • In decomposition B, the two projections are not independent of each other. • When there is more than one possibility of decomposition, use the independent projections for choosing a particular decomposition.
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Dependency Preservation Projections R1 and R2 of a relvar R are independent, if and only if both of the following are true. Every FD in R appears in one of the two projections or is a logical consequence of those in R1 and R2.
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