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Multiplicity

Multiplicity should be indicated at each end of an association. This specifies the minimum and maximum number of instances that can be linked. (E.g. a Car has 3 or 4 Wheels, but each Wheel belongs to exactly one Car). The minimum and maximum values are separated by two dots. An asterisk (*) represents an indeterminate maximum. Where the minimum and maximum are the same, the number need only be shown once. Also zero-or-more (0..*) is shortened to a simple asterisk (*) because it is so common. Finally, ranges and/or single values can be comma-separated to enumerate alternative values.

In the following diagram an Order object can be associated to only one customer but a customer can be associated to many orders.

The Order class is associated with the Customer class.