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Furthermore, there is hardly a difference between aggregations and associations during implementation, and the diagram may skip aggregation relations altogether. [9] Aggregation can occur when a class is a collection or container of other classes, but the contained classes do not have a strong lifecycle dependency on the container. The contents ...
In aggregation, the object may only contain a reference or pointer to the object (and not have lifetime responsibility for it). Sometimes aggregation is referred to as composition when the distinction between ordinary composition and aggregation is unimportant. The above code would transform into the following UML Class diagram:
UML class diagram Misuses of composition and aggregation. In object-oriented programming this relationship can be represented with a Unified Modeling Language Class diagram. This has-a relationship is also known as composition. As you can see from the Class Diagram on the right a car "has-a" carburetor, or a car is "composed of" a carburetor.
Aggregation - 1. a special type of association used to represent a stronger relationship between two classes than a regular association; typically read as "owns a", as in, "Class A owns a Class B". A hierarchy of classes where the child object may or may not continue to exist if the parent object is destroyed; see 'composition'.
Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should favor polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) over inheritance from a base or parent class. [2]
The authors further distinguish between 'Aggregation', where one object 'has' or 'is part of' another object (implying that an aggregate object and its owner have identical lifetimes) and acquaintance, where one object merely 'knows of' another object. Sometimes acquaintance is called 'association' or the 'using' relationship.
UML logo. The unified modeling language (UML) is a general-purpose visual modeling language that is intended to provide a standard way to visualize the design of a system. [1] UML provides a standard notation for many types of diagrams which can be roughly divided into three main groups: behavior diagrams, interaction diagrams, and structure ...
Also take the point about the carburetor. The diagram in the article describes this relationship as composition - but I would have thought the life-line of a carburetor is not implicitly tied to the life-line of the car (which would be the definition of composition), and so this too would be aggregation. Ultimately: I agree.