Knobit of Data modelling · K-607 · Skill

Recognises rolled-down subtypes losing supertype constraints

What it means

One table per subtype and none for the supertype. Uniqueness across subtypes cannot be declared, nothing stops one instance appearing in two subtype tables, and a relationship to the supertype has no single table to reference, so it becomes a polymorphic association (logical row 22).

How it is assessed

Flags the deficient case and passes the acceptable one. Deficient: `person` and `organisation`, no `party`; `account_holder.party_id` cannot have a foreign key; nothing stops one id being used in both tables Acceptable: A `party` table with the shared key; `person` and `organisation` keyed by `party_id` with an FK to it; exclusivity enforced by carrying the discriminator into each subtype's key, or by a DQ rule

Builds on

Recognises undeclared subtype constraintsK-519 · Skill
Explains the implementation options for subtypesK-652 · Knowledge

Needed by

None