Boyce-Codd Normal Form (BCNF)

• Hidden dependency

• Example:

  • Employee-Specialty(E#, Specialty, Manager)
  • Is in 3NF now.

• Business rules.

  • Employee may have many specialties.
  • Each specialty has many managers.
  • Each manager has only one specialty.
  • Employee has only one manager for each specialty.

• Problem is hidden relationship between manager and specialty.

  • Need separate table for manager.
  • But then we don’t need to repeat specialty.

• In real life, probably accept the duplication (specialty listed in both tables).

Employee-Specialty(E#, Specialty, Manager)

Employee(E#, Manager)

Manager(Manager, Specialty)

Employee(E#, Specialty, Manager)

Manager(Manager, Specialty)

acceptable

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