csce520-lect5 - Normalization ReadingAssignments

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Farkas CSCE 520  2 Reading Assignments Database Systems The Complete Book: Chapters 3.6, 3.7, 3.8 Following lecture slides are modified from Jeff Ullman’s slides for  Fall 2002 -- Stanford  
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Farkas CSCE 520  3 Closures Closure of attributes (A + ): find keys Closure of FDs (S + ): projection of FDs to  decompositions of schema Canonical cover:  minimize the number of  functional dependencies Important for updates
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Farkas CSCE 520  4 Canonical Cover Combine FDs if possible and eliminate  extraneous attributes: Given a set of FDs  S, and an FD X Y Attribute A is extraneous in X if S logically  implies (S-{X Y})   {(X-A) Y}.  Attribute A is extraneous in Y if the set of FDs  (S-{X Y})   {X (Y-A)} logically implies S.
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Farkas CSCE 520  5 Canonical Cover No functional dependency in S contains an  extraneous attribute Each left side of a functional dependency  in S c  is unique.
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Farkas CSCE 520  6 Example Canonical Cover Given : 1.  BC 2.  C 3.  B 4. AB   C Combine 1 and 3 into: A  BC From 2 and 4: A is extraneous in 4: B C C is extraneous in 1: A   B Result : A B, B C
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This note was uploaded on 12/13/2011 for the course CSCE 520 taught by Professor Farkas during the Spring '11 term at South Carolina.

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csce520-lect5 - Normalization ReadingAssignments

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