A natural coupling is a coupling between classes which represent concepts which are dependent in the same way.
The following couplings are natural ones:
The following couplings are artificial:
Stopwatch(time should be meaningful without a stopwatch)
Order(an order item way at least be viewed separately from the order whereas an order without any items is not an order anymore)
DatabaseConnection(an order which is not persisted is normally still an order, the dependency is not necessary from a conceptual point of view)
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