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E02Normalization - Database Design Normalization Chapter 5...

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Database Design: Normalization Chapter 5, Pratt & Adamski
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Functional Dependence An attribute A is functionally dependent  on  attribute(s) B if: given a value b for B there  is one and only one corresponding value a  for A (at a time). b 2 b 3 a 1 b 1
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Example: functional dependence All sales representatives in a given pay  class have the same commission rate. SalesRepNumber Name PayClass Commission
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Keys Primary Key:  a minimal set of attributes that  form a candidate key Any attribute or collection of attributes that  functionally determine all attributes in a  record is a Candidate Key. Note:  since no two rows in a relational table  can be duplicates, the entire record is  always a candidate key.
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Primary Key (C) C determines all attributes No subset of the attributes in C is a  candidate key A key consisting of more than one attribute  is called a “composite key.”
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Good Primary Keys Do not change over the life of the  database Are not “intelligent keys” Are not too long Do not consist of too many attributes (3 or  fewer is good)
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Foreign Keys A value in the “child” table that matches with  the related value in the “parent” table.
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