UML Class Diagrams
May 24, In a class diagram, obviously you can't have classes just floating around; it is important that you see the relationship between them. Many have. Dependency is a directed relationship which is used to show that some UML element or a set Dependency could be used on several kinds of UML diagrams . Sep 20, UML notation has quickly become an industry standard A class relationship diagram describes the types of objects in the system and.
In the following sections, I will address more important aspects of the class diagram that you can put to good use. These include interfaces, the three remaining types of associations, visibility, and other additions in the UML 2 specification. Interfaces Earlier in this article, I suggested that you think of classifiers simply as classes. In fact, a classifier is a more general concept, which includes data types and interfaces. A complete discussion of when and how to use data types and interfaces effectively in a system's structure diagrams is beyond the scope of this article.
UML Class Relationship Diagrams
So why do I mention data types and interfaces here? There are times when you might want to model these classifier types on a structure diagram, and it is important to use the proper notation in doing so, or at least be aware of these classifier types. Drawing these classifiers incorrectly will likely confuse readers of your structure diagram, and the ensuing system will probably not meet requirements. A class and an interface differ: A class can have an actual instance of its type, whereas an interface must have at least one class to implement it.
In UML 2, an interface is considered to be a specialization of a class modeling element. Example of a class diagram in which the Professor and Student classes implement the Person interface View image at full size In the diagram shown in Figure 10, both the Professor and Student classes implement the Person interface and do not inherit from it.
We know this for two reasons: As shown in Figure 10, a dotted line with a closed, unfilled arrow means realization or implementation ; as we saw in Figure 4, a solid arrow line with a closed, unfilled arrow means inheritance. More associations Above, I discussed bi-directional and uni-directional associations.
Now I will address the three remaining types of associations. Association class In modeling an association, there are times when you need to include another class because it includes valuable information about the relationship. For this you would use an association class that you tie to the primary association. An association class is represented like a normal class.
Dependency in UML
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.
Relationships in UML class 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. They are not implemented with member variables at all. Rather they might be implemented as member function arguments.
Multiplicity[ edit ] This association relationship indicates that at least one of the two related classes make reference to the other. This relationship is usually described as "A has a B" a mother cat has kittens, kittens have a mother cat. The UML representation of an association is a line connecting the two associated classes. At each end of the line there is optional notation.
For example, we can indicate, using an arrowhead that the pointy end is visible from the arrow tail. 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. CarFactory class depends on the Car class. This example in fact shows opposite to what UML specification states. CarFactory depends on the Car class.
Car class could be defined without the knowledge of CarFactory class, but CarFactory requires Car for its definition because it produces Cars.UML Chapter 4 - Relationships
It is also wrong to say that " It is possible to have a set of elements for the client or supplier. In this case, one or more arrows with their tails on the clients are connected to the tails of one or more arrows with their heads on the suppliers. A small dot can be placed on the junction if desired.