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Boyce-Codd normal form

Boyce-Codd normal form

(also BCNF)

Boyce-Codd normal form definition

BCNF is a standard for organizing database tables to minimize data repetition. If one piece of data (attribute) determines another, it should uniquely identify a row.

See also: data integrity, data deduplication, data corruption, data diddling

History of Boyce-Codd normal form

BCNF was introduced in 1974 by Raymond F. Boyce and Edgar F. Codd to improve the third normal form (3NF) for database normalization. Edgar F. Codd is renowned for formulating the relational model of data, which is the foundation of most modern database systems. While 3NF was addressing some types of redundancy, Boyce and Codd identified cases of data repetition that 3NF didn’t handle. That led to the formulation of BCNF.

How Boyce-Codd normal form works

At its core, BCNF deals with functional dependencies. A functional dependency means that one attribute’s value directly determines another attribute’s value.

For example, consider StudentID and StudentName. If every student has a unique ID, then StudentID → StudentName is a functional dependency because you can determine the StudentName from the StudentID.

Meanwhile, a superkey is a set of attributes that uniquely identifies a record in a table. It may have additional attributes that aren’t strictly necessary for identification.

For BCNF, the important thing is that if there’s a functional dependency (X → Y) in the table, then X should be a superkey. In other words, if one attribute determines another, it should uniquely identify a row.

Practical uses of BCNF

  • Redundancy elimination. Ensuring that a database is in BCNF eliminates data repetition, which, in turn, reduces the risk of data anomalies.
  • Data integrity. BCNF keeps data accurate and consistent. It ensures that data dependencies make sense and removes partial and transitive dependencies.
  • Clearer design. Database designs based on BCNF are often easier to understand and manage. They reflect a clearer understanding of the domain and its various relationships.

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