norm - 1 Normalization Anomalies Boyce-Codd Normal Form 3...

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Unformatted text preview: 1 Normalization Anomalies Boyce-Codd Normal Form 3 rd Normal Form 2 Anomalies Goal of relational schema design is to avoid anomalies and redundancy. Update anomaly : one occurrence of a fact is changed, but not all occurrences. Deletion anomaly : valid fact is lost when a tuple is deleted. 3 Example of Bad Design Drinkers(name , addr, beersLiked , manf, favBeer) name addr beersLiked manf favBeer Janeway Voyager Bud A.B. WickedAle Janeway ??? WickedAle Petes ??? Spock Enterprise Bud ??? Bud Data is redundant, because each of the ???s can be figured out by using the FDs name -> addr favBeer and beersLiked -> manf. 4 This Bad Design Also Exhibits Anomalies name addr beersLiked manf favBeer Janeway Voyager Bud A.B. WickedAle Janeway Voyager WickedAle Petes WickedAle Spock Enterprise Bud A.B. Bud Update anomaly: if Janeway is transferred to Intrepid , will we remember to change each of her tuples? Deletion anomaly: If nobody likes Bud, we lose track of the fact that Anheuser-Busch manufactures Bud. 5 Boyce-Codd Normal Form We say a relation R is in BCNF if whenever X -> A is a nontrivial FD that holds in R , X is a superkey. Remember: nontrivial means A is not a member of set X . Remember, a superkey is any superset of a key (not necessarily a proper superset). 6 Example Drinkers(name , addr, beersLiked , manf, favBeer) FDs: name->addr favBeer, beersLiked->manf...
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This note was uploaded on 08/01/2008 for the course CSC 540 taught by Professor Chirkova during the Spring '08 term at N.C. State.

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norm - 1 Normalization Anomalies Boyce-Codd Normal Form 3...

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