Functional dependency: Difference between revisions

Revision as of 21:37, 3 March 2020

Revision as of 16:31, 20 June 2020

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=== Cars ===

Suppose one is designing a system to track vehicles and the capacity of their engines. Each vehicle has a unique [[vehicle identification number]] (VIN). One would write ''VIN'' → ''EngineCapacity'' because it would be inappropriate for a vehicle's engine to have more than one capacity. (Assuming, in this case, that vehicles only have one engine.) TransverselyOn the other hand, ''EngineCapacity'' → ''VIN'' is incorrect because there could be many vehicles with the same engine capacity.

This functional dependency may suggest that the attribute EngineCapacity be placed in a relation with [[candidate key]] VIN. However, that may not always be appropriate. For example, if that functional dependency occurs as a result of the [[transitive relation|transitive]] functional dependencies VIN → VehicleModel and VehicleModel → EngineCapacity then that would not result in a normalized relation.