Design Codes: UML Class Diagram: Association, Aggregation and Composition
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. Oct 9, explanations. Explanations about every relationship in UML class diagrams. The composition is a variation of the aggregation relationship. Aggregation. Aggregation Relationship. Aggregation. refers to the formation of a particular class as a result of one class being.
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.
UML Association vs Aggregation vs Composition
Differences between Composition and Aggregation[ edit ] Composition relationship 1. When attempting to represent real-world whole-part relationships, e. 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. In practice, means that any instance of the subtype is also an instance of the superclass. An exemplary tree of generalizations of this form is found in biological classification: The relationship is most easily understood by the phrase 'an A is a B' a human is a mammal, a mammal is an animal. The UML graphical representation of a Generalization is a hollow triangle shape on the superclass end of the line or tree of lines that connects it to one or more subtypes.
The generalization relationship is also known as the inheritance or "is a" relationship. The superclass base class in the generalization relationship is also known as the "parent", superclass, base class, or base type. The subtype in the specialization relationship is also known as the "child", subclass, derived class, derived type, inheriting class, or inheriting type.
oop - Aggregation in class diagram and class properties - Stack Overflow
Note that this relationship bears no resemblance to the biological parent—child relationship: A is a type of B For example, "an oak is a type of tree", "an automobile is a type of vehicle" Generalization can only be shown on class diagrams and on use case diagrams. The UML graphical representation of a Realization is a hollow triangle shape on the interface end of the dashed line or tree of lines that connects it to one or more implementers.
A plain arrow head is used on the interface end of the dashed line that connects it to its users. In component diagrams, the ball-and-socket graphic convention is used implementors expose a ball or lollipop, whereas users show a socket.
my kingdom for a smile :-): UML Class Diagram Relationships, Aggregation, Composition
Realizations can only be shown on class or component diagrams. A realization is a relationship between classes, interfaces, components and packages that connects a client element with a supplier element.
One class depends on another if the independent class is a parameter variable or local variable of a method of the dependent class. This is different from an association, where an attribute of the dependent class is an instance of the independent class.
Sometimes the relationship between two classes is very weak. For example, a department with employees. A stronger 'ownership' relationship.
A car and a wheel. The car 'entirely contains' the wheel. The Wheel instance won't continue living without the Car instance containing it. Is this a reasonable differentiation?Class Diagram: Association & Aggregation Relationships - Georgia Tech - Software Development Process
Yes, that is a reasonable definition. Just remember that others may not share that definition and that you might need to explain your use of aggregation to them. The definition I'm using?
The 'has a collection of' definition? Association and composition are fairly straightforward. Aggregation is the wobbly one. In practice, I find that the 'part of' test is works well 'ownership' is a sub-optimal way to think about it.
A person can be part of a club, thus a club aggregates people it does not own them. When the club is destroyed the people continue to exist.