Example: Customers & Orders
From the CUSTOMER perspective:
- a customer may make many orders (M orders of 1:M connectivity)
- a customer does not necessarily make orders (optional participation of orders, cardinality is (0,N))
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From the ORDER perspective:
- an order is made by (associated with) one and only one customer (1 customer of 1:M connectivity)
- an order must be made by (associated with) a customer (mandatory participation, cardinality is (1,1))