Knobit of Data modelling · K-514 · Skill

Recognises a lossy decomposition

What it means

An entity is split so that joining the parts back produces rows that never existed. The split is lossless only if the shared attributes are a key of at least one part.

How it is assessed

Flags the deficient case and passes the acceptable one. Deficient: Account Holder split into (Account, Holder Role) and (Party, Holder Role) and joined on Holder Role: two accounts each with one joint holder give four holdings Acceptable: Keep (Account, Party, Holder Role) whole, or split only on attributes that are a key of one side

Builds on

Explains lossless-join decompositionK-563 · Knowledge

Needed by

Recognises a lossy or unconstrained vertical splitK-604 · Skill