Backend & systems·Data modelling and storage engines
you store the customer's address in exactly one table so that changing it cannot leave four stale copies behind.
Normalisation
Also callednormalization, third normal form
Structuring tables so each fact is stored once, with relationships expressed by keys rather than repetition. It makes writes correct by construction: there is no second copy to forget. The cost is joins on the read path, which is why every normalised schema eventually meets a report that needs six of them.