Databases
Normalisation
Organising tables so that each fact is stored once, reducing redundancy at the cost of more joins.
Normal forms (1NF through 5NF) are a series of rules that progressively eliminate duplication. In practice, most schemas aim for third normal form (3NF): every non-key column depends on the key, the whole key, and nothing but the key. Denormalisation - deliberately adding redundancy - is a performance trade-off, not a design failure, but it must be maintained consciously or the copies drift.