Recognises a lossy or unconstrained vertical split
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.
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What it looks like in practice
Expected result: The split and its missing key or constraint
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
Also known as: Lossy or unconstrained vertical split (physical model)
Related knobits
Builds on
All 40 knobits of Design the physical data model.
Source: Review checklist 06-physical, row 4; Heath 1971; Rissanen 1977; S&W 12.6; E&N 17.7