Objects are connected via links, which are instances of associations between the classes of the objects being considered. The concrete representation of a structure by objects is often more revealing than the abstract representation of a structure using classes, especially in the case of recursive structures. The object diagram below illustrates a portion of the general structure of cars. Each car has an engine and four wheels (excluding the spare wheel!).
This diagram is an instance of the following class diagram:
Links that are instances of reflexive associations may connect an object to itself. In this case, the link is represented by a loop attached to a single object. The following example illustrates two links that are instances of the same reflexive association. The first link shows that Etienne is Jean-Luc's boss, the second link shows that Denis is his own boss.
Most links are binary. However, there exist some links that may connect together more than two objects — those that correspond to ternary relationships, for instance. The representation of ternary relationships may be combined with the other notation elements: the diagram below represents a family of ternary links that are instances of a ternary association with multiplicity
on the N
class side. This notation has the advantage of removing any ambiguities inherent to the representation of multiplicity for non-binary associations.Student
Example of a combination of notation elements in order to represent multiple ternary relationships in a condensed way.
© 1997 Editions, Eyrolles, Paris, France . All rights reserved.