Relationships in UML class diagrams
UML Class Diagram Tutorial; What is a Class; UML Class Notation; Perspectives of Class Diagram; Relationships between classes; Class Diagram Example. In UML, a relationship is a connection between model elements. A UML relationship is a type of model element that adds semantics to a model by defining the. A relationship is a general term covering the specific types of logical connections found on class and object diagrams. UML.
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.
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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.
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.
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In component diagrams, the ball-and-socket graphic convention is used implementors expose a ball or lollipop, whereas users show a socket. 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.
Relationships in UML
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. Dependency relationship overview diagram - usage, abstraction, deployment.
Usage is a dependency in which one named element client requires another named element supplier for its full definition or implementation.UML Tutorial: Association, Aggregation, Composition, Dependency, Generalization, and Realization
The abstraction relates two elements representing the same concept but at different levels of abstraction. The deployment is a dependency which shows allocation deployment of an artifact to a deployment target. It is not very clear why UML 2. Note, that UML 2. An experienced software developer knows what happens at runtime when some dependency is missing, with application killed by LinkageError or ClassNotFoundException from the class loader.
So dependency could in fact have some grave runtime semantics implications. A dependency is generally shown as a dashed arrow pointing from the client dependent at the tail to the supplier provider at the arrowhead. The arrow may be labeled with an optional stereotype and an optional name.
Class SearchController depends on requires SiteSearch interface. For many years UML specifications provide contradictory example of the dependency shown below.
- UML Class Relationship Diagrams
- Dependency in UML
- UML Composition
The explanation for the Figure 7. In this case, the dependency is an instantiate dependency, where the Car class is an instance of the CarFactory class. Car class has a dependency on the CarFactory class.