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

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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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This note was uploaded on 04/01/2012 for the course CSE,IT 101 taught by Professor Mirunaalini during the Spring '12 term at Indian Institute of Technology, Chennai.

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

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