The multiplicity of an association end is the number of possible instances of the class associated with a single instance of the other end. Multiplicities are single numbers or ranges of numbers. In our example, there can be only one Customer for each Order , but a Customer can have any number of Orders . This table gives the most common multiplicities. The notation n . .
Every class diagram has classes, associations, and multiplicities.
Navigability and roles are optional items placed in a diagram to provide clarity. Packages and object diagrams To simplify complex class diagrams, you can group classes into packages . A package is a collection of logically related UML elements. The diagram below is a business model in which the classes are grouped into packages. Packages appear as rectangles with small tabs at the top.