Chapter14-FunctionalDependencies.pptx

B decomposing the emp relation into two 4nf relations

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b. Decomposing the EMP relation into two 4NF relations EMP_PROJECTS and EMP_DEPENDENTS. c. The relation SUPPLY with no MVDs is in 4NF but not in 5NF if it has the JD(R1, R2, R3). d. Decomposing the relation SUPPLY into the 5NF relations R1, R2, R3 Functional Dependencies and Normalization 53
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Join Dependencies and Fifth Normal Form A join dependency ( JD ), denoted by JD( R 1 , R 2 , ..., R n ), specified on relation schema R , specifies a constraint on the states r of R . The constraint states that every legal state r of R should have a non-additive join decomposition into R 1 , R 2 , ..., R n ; that is, for every such r we have * ( R1 ( r ), R2 ( r ), ..., Rn ( r )) = r Note : an MVD is a special case of a JD where n = 2. A join dependency JD( R 1 , R 2 , ..., R n ), specified on relation schema R , is a trivial JD if one of the relation schemas R i in JD( R 1 , R 2 , ..., R n ) is equal to R . Functional Dependencies and Normalization 54
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Join Dependencies and Fifth Normal Form Definition: A relation schema R is in fifth normal form ( 5NF ) (or Project- Join Normal Form ( PJNF )) with respect to a set F of functional, multivalued, and join dependencies if, for every nontrivial join dependency JD( R 1 , R 2 , ..., R n ) in F + (that is, implied by F ), every R i is a superkey of R . Discovering join dependencies in practical databases with hundreds of relations is next to impossible. Therefore, 5NF is rarely used in practice . Functional Dependencies and Normalization 55
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Summary Informal Design Guidelines for Relational Databases Functional Dependencies (FDs) Normal Forms (1NF, 2NF, 3NF)Based on Primary Keys General Normal Form Definitions of 2NF and 3NF (For Multiple Keys) BCNF (Boyce-Codd Normal Form) Fourth and Fifth Normal Forms Functional Dependencies and Normalization 56
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  • Fall '09
  • SUNANHAN
  • Database normalization, BCNF

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