Knobit of Data modelling · K-610 · Skill

Recognises a surrogate key without natural-key uniqueness

What it means

A system-generated primary key added and the natural key not made a unique constraint. Nothing then stops the same thing being recorded twice. The physical form of logical row 18.

How it is assessed

Flags the deficient case and passes the acceptable one. Deficient: `party` with `party_id` as identity primary key and `registry_code` with no unique constraint; a reload registers every company again Acceptable: `uk_party_registry_code` (with the identifier type, where the logical model has one); `PHY-020` adds the surrogate, the unique constraint is added by hand (`ANO-012` when a uniqueness rule claims schema enforcement, `PHY-016` for type-2 dimensions)

Builds on

Recognises an entity identified only by a system-assigned keyK-518 · Skill
Explains natural keys, surrogate keys and key stabilityK-568 · Knowledge

Needed by

None