Recognises a join dependency kept in one entity
A three-way entity that can be rebuilt from its pairwise projections because of a cyclic business rule, kept as one entity; or the reverse, three pairwise entities joined as if the rule held when it does not.
Can AI do this?
Not tested yet
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What it looks like in practice
Expected result: The three-way entity and the cyclic rule that does or does not make it decomposable
How it is assessed: Flags the deficient case and passes the acceptable one. Deficient: Branch Channel Product as one entity, although the rule is that a branch offers every product it is authorised for through every channel it operates; one new authorisation needs a row per channel Acceptable: Three entities (Branch Channel, Channel Product, Branch Product) when the cyclic rule holds, recorded as a data rule; the three-way entity when it does not
Also known as: Join dependency (5NF) (logical model)
Related knobits
Builds on
All 56 knobits of Derive the logical data model.
Source: Review checklist 05-logical, row 13; Fagin 1979; Kent 1983; S&W 13.4