Crisp Reading Notes on Latest Technology Trends and Basics

Database Normal Forms

http://www.bkent.net/Doc/simple5.htm#label4.1

First Normal Form

  • A Relational Database is a table of Atomic Values
  • Every record contains the same number of fields
  • Lists must be flattened out
  • The First Normal Form is responsible for causing various Redundancies, that other Normal Forms try to remove

Second Normal Form

  • Every non Primary-key column must fully depend on all the Primary-Key columns
  • If a Value column Vj depends on keys <K1, K2, …, Kn>,
    • then a separate table of < K1, K2, …, Kn, Vi >  must be created

Third Normal Form

  • There must be no dependencies among non Primary-Key fields
  • If a Value column Vi depends on column Vj, then
    • A separate table Vj must be created

Boyce-Codd Normal Form

  • There must be no dependencies from non-keys to any portion of the keys
  • That is, there must be no dependencies from the non-keys
  • Cannot decompose a 3NF to a BCNF, while preserving dependencies

Fourth Normal Form

  • Two independent multi-valued attributes must not be present in the same table
  • If keys <K1, K2, …, Kn > have two multi-valued columns Vi and Vj
    • Then separate tables – < K1, K2, …, Kn, Vi >  and < K1, K2, …, Kn, Vj > must be created

Fifth Normal Form

  • This applies to decomposition of a table with only keys
  • If there are multivalued relationships, among the candidate keys, then they may be decomposed into Fifth Normal Form.
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