Database Normalisation

• A database design technique used to reduce data redundancy and eliminate insertion, deletion and update anomalies
• Ensures logical storage of data

Database normalisation forms §

• 1 NF
  • Single-valued attributes - atomic value
  • Each table cell should have only one value
  • Each record should be unique
• 2 NF
  • Should be in 1 NF
  • No Partial dependency: No non-prime attribute should be dependent on a proper subset of the candidate key
• 3 NF
  • Should be in 2 NF
  • No transitive dependency: An attribute is dependent on another non-key attribute, which is itself dependent on the candidate key
  • To be in 3-NF, in every non-trivial functional dependency X -> Y in the relation, at least one of the below conditions should be true
    • X is a super key (i.e, the candidate key or a super set of it)
    • Y is a prime attribute (part of the candidate key)
• Boyce-Codd Normal Form / BCNF
  • Should be in 3 NF
  • In every non-trivial functional dependency X -> Y in the relation,
    • X is a super key
• 4 NF
• 5 NF
• 6 NF

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Related §

• Partial dependency
• Functional Dependency

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Refs §

1. How normalisation prevents Database anomalies
2. https://condor.depaul.edu/gandrus/240IT/accesspages/normalization3.htm#:~:text=Basically%2C%20normalization%20is%20the%20process,related%20data%20in%20a%20table