Fourth Normal Form (4NF)

Concepts covered: 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

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This section is part of the Beyond 3NF lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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