UML 2 Class Diagram Guidelines
Essential elements of A UML class diagram; Relationships; Aggregation vs. This Diagram includes the class name, attributes, and operation in separate Allows drawing detailed charts which highlights code required to be. In software engineering, a class diagram in the Unified Modeling Language ( UML) is a type of In the diagram, classes are represented with boxes that contain three compartments: . The UML representation of a composition relationship shows composition as a filled diamond shape on the containing class end of the lines. As mentioned earlier, the purpose of the class diagram is to show the types being The UML representation of a class is a rectangle containing three .. The composition aggregation relationship is just another form of the.
When representing a software or database relationship, e.
UML Class Diagram Tutorial with Examples
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.
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. 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.
Class diagram - Wikipedia
They are not implemented with member variables at all. Both Company and Departments are modeled as classes, and a department cannot exist before a company exists. Here the Department class's instance is dependent upon the existence of the Company class's instance.
Let's explore basic aggregation and composition aggregation further. Basic aggregation An association with an aggregation relationship indicates that one class is a part of another class.
In an aggregation relationship, the child class instance can outlive its parent class. To represent an aggregation relationship, you draw a solid line from the parent class to the part class, and draw an unfilled diamond shape on the parent class's association end.
Figure 12 shows an example of an aggregation relationship between a Car and a Wheel. Example of an aggregation association View image at full size Composition aggregation The composition aggregation relationship is just another form of the aggregation relationship, but the child class's instance lifecycle is dependent on the parent class's instance lifecycle.
In Figure 13, which shows a composition relationship between a Company class and a Department class, notice that the composition relationship is drawn like the aggregation relationship, but this time the diamond shape is filled. Example of a composition relationship View image at full size In the relationship modeled in Figure 13, a Company class instance will always have at least one Department class instance.
Another important feature of composition aggregation is that the part class can only be related to one instance of the parent class e. Reflexive associations We have now discussed all the association types. As you may have noticed, all our examples have shown a relationship between two different classes.
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However, a class can also be associated with itself, using a reflexive association. This may not make sense at first, but remember that classes are abstractions. When a class is associated to itself, this does not mean that a class's instance is related to itself, but that an instance of the class is related to another instance of the class.
Example of a reflexive association relationship The relationship drawn in Figure 14 means that an instance of Employee can be the manager of another Employee instance.
However, because the relationship role of "manages" has a multiplicity of Visibility In object-oriented design, there is a notation of visibility for attributes and operations. For example it makes sense to say that a room is part of a building, it doesn't make sense to say that an address is part of a person. Another good indication that composition makes sense is when the lifecycle of the part is managed by the whole -- for example a plane manages the activities of an engine.
When deciding whether to use composition over association, Craig Larman says it best: If in doubt, leave it out. Unfortunately many modelers will agonize over when to use composition when the reality is little difference exists among association and composition at the coding level.
A vocabulary defines the semantics of entity types and their responsibilities, the taxonomical relationships between entity types, and the ontological relationships between entity types. Semantics is simply a fancy word for meaning - when we're defining the semantics of something we're defining it's meaning.
Taxonomies are classifications of entity types into hierarchies, an example of which is presented for persons Figure 9.
UML Class Diagram Tutorial with Examples
Ontology goes beyond taxonomy. Where taxonomy addresses classification hierarchies ontology will represent and communicate knowledge about a topic as well as a set of relationships and properties that hold for the entities included within that topic.
A taxonomy for people within the university. The semantics of your conceptual model are best captured in a glossary. There are several interesting aspects of Figure 9: It uses UML 2. There are three generalization sets for Person: