Fourth Normal Form (4NF)

Concepts: dmFourthNormalForm

4NF: Separate Independent Multi-Valued Facts 4NF handles multi-valued dependencies: when an entity has two or more independent multi-valued attributes. A person can speak multiple languages AND play multiple instruments. These two facts are independent of each other. Storing them in the same table creates a cartesian product. If Alice speaks English and Spanish, and plays piano and guitar, a single table creates four rows: (Alice, English, piano), (Alice, English, guitar), (Alice, Spanish, piano), (Alice, Spanish, guitar). But Alice speaking Spanish has nothing to do with her playing guitar. These are independent facts forced into the same row. The fix: two separate tables. person_languages (person, language) and person_instruments (person, instrument). Each multi-valued dependency gets it