Recognises a partial dependency on a composite key

K-508 · Skill knobit · Activity: Derive the logical data model · Competence: Data modelling

In an entity with a composite key, a non-key attribute depends on only part of the key.

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What it looks like in practice

Expected result: The non-key attribute and the part of the key it depends on

How it is assessed: Flags the deficient case and passes the acceptable one. Deficient: Instalment keyed by (Loan Identifier, Instalment Number) carries Loan Maturity Date, which depends on Loan Identifier alone Acceptable: Loan Maturity Date on Loan; Instalment holds only facts about the instalment (LOG-019)

Also known as: Partial dependency (2NF) (logical model)

Related knobits

Builds on

• K-555 Explains second normal form

Usually followed by

• K-533 Decomposes an entity along a functional dependency without loss

All 56 knobits of Derive the logical data model.

Source: Review checklist 05-logical, row 8; Codd 1971; Kent 1983; S&W 2.7