Class diagram - Wikipedia
UML composite aggregation (composition) relationship means that at most one composite object has responsibility for the existence and storage of the. A UML relationship is a type of model element that adds semantics to a that are generalizations and realizations, and those that have dependencies on other. A realize relation is used to either an > or to an abstract class. Simply use two relationships - one showing a generalization and a second showing.
Association end query is owned by classifier QueryBuilder and association end qbuilder is owned by association Builds itself The "ownership" dot may be used in combination with the other graphic line-path notations for properties of associations and association ends. These include aggregation type and navigability. UML standard does not mandate the use of explicit end-ownership notation, but defines a notation which shall apply in models where such use is elected.
The dot notation must be applied at the level of complete associations or higher, so that the absence of the dot signifies ownership by the association. In other words, in binary associations the dot will be omitted only for the ends which are not owned by a classifier.
Attribute notation can be used for an association end owned by a class, because an association end owned by a class is also an attribute. This notation may be used in conjunction with the line arrow notation to make it perfectly clear that the attribute is also an association end. Association end qb is an attribute of SearchService class and is owned by the class.
Navigability End property of association is navigable from the opposite end s of association if instances of the classifier at this end of the link can be accessed efficiently at runtime from instances at the other ends of the link.
UML specification does not dictate how efficient this access should be or any specific mechanism to achieve the efficiency. It is implementation specific. When end property of association is marked as not navigable, in [UML 2. An end property of association that is owned by an end class, or that is a navigable owned end of the association indicates that the association is navigable from the opposite ends; otherwise, the association is not navigable from the opposite ends.
This definition is odd because it makes navigability strongly dependent on ownership, while these are assumed to be orthogonal concepts; some examples in UML 2.
A2 has unspecified navigability while B2 is navigable from A2. A3 is not navigable from B3 while B3 has unspecified navigability. It is an association that represents a part-whole or part-of relationship. As shown in the image, a Professor 'has a' class to teach. As a type of association, an aggregation can be named and have the same adornments that an association can.
However, an aggregation may not involve more than two classes; it must be a binary association. Furthermore, there is hardly a difference between aggregations and associations during implementation, and the diagram may skip aggregation relations altogether. The contents of the container still exist when the container is destroyed. In UMLit is graphically represented as a hollow diamond shape on the containing class with a single line that connects it to the contained class.
The aggregate is semantically an extended object that is treated as a unit in many operations, although physically it is made of several lesser objects. Here the student can exist without library, the relation between student and library is aggregation.
Composition[ edit ] Two class diagrams. The diagram on top shows Composition between two classes: A Car has exactly one Carburetor, and a Carburetor has at most one Car Carburetors may exist as separate parts, detached from a specific car.
The diagram on bottom shows Aggregation between two classes: A Pond has zero or more Ducks, and a Duck has at most one Pond at a time.
The UML representation of a composition relationship shows composition as a filled diamond shape on the containing class end of the lines that connect contained class es to the containing class. Differences between Composition and Aggregation[ edit ] Composition relationship 1. When attempting to represent real-world whole-part relationships, e.
UML Association vs Aggregation vs Composition
When the container is destroyed, the contents are also destroyed, e. When representing a software or database relationship, e. When the container is destroyed, the contents are usually not destroyed, e. Thus the aggregation relationship is often "catalog" containment to distinguish it from composition's "physical" containment.
A single student can associate with multiple teachers: The example indicates that every Instructor has one or more Students: We can also indicate the behavior of an object in an association i. Association vs Aggregation vs Composition The question "What is the difference between association, aggregation and composition" has been frequently asked lately.
Actually, Aggregation and Composition are subsets of association meaning they are specific cases of association.
In both aggregation and composition object of one class "owns" object of another class. But there is a subtle difference: Aggregation implies a relationship where the child can exist independently of the parent.
Class parent and Student child.
UML Association vs Aggregation vs Composition
Delete the Class and the Students still exist. Composition implies a relationship where the child cannot exist independent of the parent. House parent and Room child.
Rooms don't exist separate to a House.