Detailed Note

DBMS — Normalisation in Simple Language

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~8 min read

Normalisation

Normalisation organises data so each fact lives in exactly one place.

Why it matters

A student table that repeats a department name 500 times will eventually disagree with itself. Split it: Students (id, name, dept_id) + Departments (dept_id, name).

1NF, 2NF, 3NF, BCNF

  • 1NF: Atomic values, no repeating groups.
  • 2NF: 1NF + no partial dependency on part of a key.
  • 3NF: 2NF + no transitive dependency (non-key → non-key).
  • BCNF: Every determinant is a superkey — stricter than 3NF.

Exam trick

If a non-key attribute depends on only part of a composite key, it is a 2NF violation. If it depends on another non-key attribute, it is a 3NF violation.