DEV475 Mastering Object-Oriented Analysis and Design with UML ...

Module 6 - Use-Case AnalysisWhat Does Multiplicity Mean?What Does Multiplicity Mean?• Multiplicity answers two questions:• Is the association mandatory or optional?• What is the minimum and maximum number ofinstances that can be linked to one instance?CourseOffering0..* 1Course0..*preRequisites 0..3Mastering Object Oriented Analysis and Design with UMLCopyright © 2003 Rational Software, all rights reserved 49• Multiplicity lets you know the lower and the upper bound number ofrelationships that a given object can have with another object. Many times youdo not know what the maximum number of instances may be, and you will usethe “*” to specify that this number is unknown.• The most important question that multiplicity answers: Is the association ismandatory? A lower bound number that is greater than zero indicates that therelationship is mandatory.• This example indicates that a course object can be related to zero or more courseofferings. You can tell that the relationship is optional because the lower boundnumber is zero. The upper bound number of the relationship is unknown, asindicated by the “*”. If you read the association the other way, you will see that agiven course offering object can be related to only one course. This relationship ismandatory and indicates that it is not possible for a course offering object to existwithout an associated course object.6 - 49