UML 2 Class Diagram Guidelines
Aggregation can occur when a class is a collection or container of other In Inheritance relationship a class is derived from another class. These are all examples of the concept of aggregation, which represents "is part of " jingle-bells.info engine is part. In software engineering, a class diagram in the Unified Modeling Language ( UML) is a type of . Aggregation is a variant of the "has a" association relationship; aggregation is more specific than association. It is an association that represents a.
In case arrow is on the both sides, association has bidirectional association. We can indicate the multiplicity of an association by adding multiplicity adornments to the line denoting the association.
The example indicates that a Student has one or more Instructors: 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.
Delete the Class and the Students still exist. It has a risk-value delivery lifecycle, is goal-driven, is enterprise aware, and provides the foundation for scaling agile. This book is particularly important for anyone who wants to understand how agile works from end-to-end within an enterprise setting. Data professionals will find it interesting because it shows how agile modeling and agile database techniques fit into the overall solution delivery process.
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Furthermore, this book describes the fundamental programming and testing techniques for successful agile solution delivery. 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.
Class diagram - Wikipedia
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.
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: