Object-Oriented Software Development with UML - UNU-IIST ...

Conceptual Model – Associations 55*Tzero or more; "many’’5Texactly five1..*Tone or more; ‘‘at least one’’3,5,8Texactly three, five or eight1..40Tone to fortyPersonPersonOne person mayhave any numberof jobs or no job.Works-for**Works-forEach person worksfor one and only onecompnay*1CompnayCompnayFigure 5.6: Multiplicity valuesRoles of associationsEach end of an association 1 is called a role of the association, which may has a role name. Naming a rolein a conceptual model is sometimes useful. For example, the role names boss and worker distinguish twoemployees who work for a company and participate in the Manages association (See Figure 5.8).When we come up to the design and implementation of the system, roles provide a way of viewing anassociation as a traversal from one object to a set of associated objects.The purpose of an association and a link between two objects Objects may have many sorts of relationship,and thus classes (or concepts) may have all sorts of associations in a problem domain. Whetheran association is useful or not depends on whether it fulfill the following purpose.of the classes.=An association between two classes is to provide physical or conceptual connections between objects=Only objects that are associated with each other can collaborate with each other through the links.Booch describes the role of a link between objects as follows:“A link denotes the specific association through which one object (the client) applies the servicesof another object (the supplier), or through which one object may navigate to another”.1 In this course, we are mainly concerned with binary associations which relate two classes. In general, an association may beternary or even higher order which relate three or more classes.Report No. 259, July 2002UNU/IIST, P.O. Box 3058, Macau