Boyce–Codd normal form

Boyce–Codd normal form (or BCNF or 3.5NF) is a normal form used in database normalization. It is a slightly stronger version of the third normal form (3NF). BCNF was developed in 1974 by Raymond F. Boyce and Edgar F. Codd to address certain types of anomalies not dealt with by 3NF as originally defined.

Not to be confused with Backus–Naur form.

If a relational schema is in BCNF then all redundancy based on functional dependency has been removed, although other types of redundancy may still exist. A relational schema R is in Boyce–Codd normal form if and only if for every one of its dependencies X → Y, at least one of the following conditions hold:

  • X → Y is a trivial functional dependency (Y ⊆ X),
  • X is a superkey for schema R.

Note that if a relational schema is in BCNF, then it is in 3NF.

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