Skilirium

Stage 6: Design the physical data model

Knobit of Data modelling · K-604 · Skill

Recognises a lossy or unconstrained vertical split

What it means

One entity split into two tables for width or access, where the tables do not share the key, or the one-to-one relationship between them is not enforced. Joining back produces rows that never existed, or one row gets two extensions. A dependency spanning both parts has no key to enforce it.

How it is assessed

Flags the deficient case and passes the acceptable one. Deficient: `account` and `account_interest_terms`, the second with its own surrogate and joined on the product code: two accounts on one product give four rows. Or `account_interest_terms.account_id` with an FK but no unique constraint Acceptable: Both tables keyed on `account_id`; in the extension the primary key is also the foreign key, so one-to-one is enforced; whether the extension is optional is stated

Builds on

Needed by

  • None