Gilbert and McCarty describe cardinality as the number of objects that participate in an association and whether the participation is optional or mandatory. To determine cardinality, ask the following questions:

  • Which objects collaborate with which other objects?

  • How many objects participate in each collaboration?

  • Is the collaboration optional or mandatory?

For example, let's consider the following example. We are creating an Employee class that inherits from Person, and has relationships with the following classes:

  • Division

  • JobDescription

  • Spouse

  • Child

What do these classes do? Are they optional? How many does an Employee need?

  • Division

    • This object contains the information relating to the division that the employee works for.

    • Each employee ...

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