L21 - Design2 - On Monday On Monday We Started Looking at...

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Unformatted text preview: On Monday On Monday We Started Looking at We Started Looking at Relational Database Design Relational Database Design We looked at some example scenarios and saw that some of them were not good That motivated a desire to develop a theory to Decide whether a particular relation R is in good form. In the case that a relation R is not in good form, decompose it into a set of relations { R 1 , R 2 , ..., R n } such that each relation is in good form the decomposition is a lossless-join decomposition theory is based on functional dependencies and multivalued dependencies First normal form all attributes in a relation R are atomic Definition of what it means for a functional dependency to hold on a relation R a functional dependency holds on a relation schema R iff for any legal relation r(R) with R and R, t 1 [ ] = t 1 [ ] t 2 [ ] = t 2 [ ] On Monday On Monday cont. (i) cont. (i) We defined two normal forms: Boyce Codd Normal Form (BCNF) a relation schema R is in BCNF with respect to a set F of fds if, for all fds in F + (the closure of F) of the form with R and R at least one of the following holds: is trivial (that is, ) is a superkey for R Third Normal Form (3NF) a relation schema R is in BCNF with respect to a set F of fds if, for all fds in F + of the form with R and R at least one of the following holds: is trivial (that is, ) is a superkey for R each attribute A in is contained in a candidate key for R On Monday On Monday cont. (ii) cont. (ii) We saw how to decompose a relation schema R into BCNF: given a non-trivial dependency that causes a violation of BCNF, decompose R into: ( ) (R ( )) We observed that it is not always possible to decompose R into BCNF and still have a dependency preserving decomposition (and this actually motivated the decision to look at 3NF) Remember: Remember: Goals of Normalization Goals of Normalization Suppose that R is a relation scheme with a set F of functional dependencies....
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This note was uploaded on 04/08/2008 for the course EE 468 taught by Professor Conry during the Spring '08 term at Clarkson University .

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L21 - Design2 - On Monday On Monday We Started Looking at...

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