We write object-class cardinality constraints in the same format as participation constraints and place them inside the top right-hand corner of the object-class rectangle. Shorthand notation may also be used so that if the minimum and maximum values are identical, only a single number or variable need be shown. When an object-class cardinality constraint is not specified, we assume the constraint to be 0:*.
Figure 1. An object-class cardinality constraint
Figure 1 shows an example of an object-class cardinality constraint. There are exactly 50 states in the USA. Hence, the object-class cardinality constraint for the State in the USA object class is 50.
Here is a short quiz so you can test your understanding of object-class cardinality constraints.
Go to the OSA Tutorial ORM Constraints
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Last updated 22 Sept 1994. by Mingkang Xu (email@example.com), Lei Cao(firstname.lastname@example.org)