CODEWITHSUNDEEP
sqldatabase-normalization
little m
little m

Reputation: 113

When should fifth normal form (5NF) structure be used?

When should fifth normal form (5NF) structure be used?

Upvotes: 4

Views: 1952

Answers (3)

Dominik Kierner
Dominik Kierner

Reputation: 13

5NF deals with the reconstruction of information from smaller bits of information and ensures that information can be composed from joins without redundancies, by requiring that every join dependency has only superkey components.

The more joined relations and attributes you have when creating a join, i. e. the higher your join complexity, the more important 5NF becomes, as the likelihood of overlaps between independent attribute combinations only increases with the number of possible combinations. N-way joins where n > 2 often involve closely related data and have therefore an increased likelihood of containing such anomalies.

5NF normalization itself might also be implicitly achieved under the right conditions for existing 3NF and BCNF tables, according to Fagin's and C. J. Date's proofs in "Simple Conditions for Guaranteeing Higher Normal Forms in Relational Databases", p. 469:

  • 3NF and every key is simple ⟹ 5NF
  • BCNF and some key is simple ⟹ 4NF

Upvotes: -2

Nikhil Vartak
Nikhil Vartak

Reputation: 5127

When to use the fifth normal form (5NF)?

Only during interviews, not in real. That's extreme. Even during interview you are asked to explain database normalization, you are really not expected to go till 5th one. First 3 and you will be selected. :)

Upvotes: -1

Randy Minder
Randy Minder

Reputation: 48522

This is more or less a subjective topic. But my subjective opinion is that the 5NF is really more of a theoretical concept than a practical one. I've been developing databases for 20+ years and have never gone to that extent, or ever wanted to.

In practice it means that your database is already in 4NF and cannot be further decomposed without loss of data.

Upvotes: 0

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