UML

Structural Diagram

Class Diagram

Class Diagram

• To describe the types of objects in a system and their relationships.

• The classes in a class diagram represent both the main objects and or interactions in the application and the objects to be programmed.

• In the class diagram, classes are represented with boxes which contain three parts– The upper part holds the name of the class

– The middle part contains the attributes of the class, and

– The bottom part gives the methods or operations the class can take or undertake

Example of a Class

Figure 1: Class Customer

Figure 2: Class BankAccount

Relationships between Classes

• Used– during requirements analysis to model application domain

concepts

– during system design to model subsystems

– during object design to specify the detailed behavior and attributes of classes

• There are several relationships that might exist between classes. These includes:– Association

– Aggregation

– Generalization

Association

• The association relationship is the most common relationship in a class diagram. It shows the relationship between instances of classes.

• For example, the class Order is associated with the class Customer.

• The multiplicity of the association denotes the number of objects that can participate in the relationship. For example, an Order object can be associated to only one customer, but a customer can be associated to many orders.

Figure 3: Example of Association relationship

1-to-1 and 1-to-many Associations

Figure 5: 1-to-many association

Polygon

draw()

Point

x: Integer

y: Integer

*

Country

name:String

Capital

name:String

11

Figure 4: 1-to-1 association

Many-to-many Associations

StockExchange Company

tickerSymbolLists

**

• A stock exchange lists many companies.• Each company is identified by a ticker symbol

Figure 6: Many-to-many association

Aggregation

A variant of the "has a" or association relationship; aggregation is more specific than association. It is an association that represents a part-whole or part-of relationship

Graphically represented as a hollow diamond shape on the containing class

For example, we can think of Car as a whole entity and Car Wheel as part of the overall Car.

Figure 7: Example of Aggregation relationship

cont.. Aggregation

• A solid diamond denotes composition: A strong form of aggregation where the life time of the component instances is controlled by the aggregate. That is, the parts don’t exist on their won (“the whole controls/destroys the parts”)

TicketMachine

ZoneButton

3

Figure 8: Example of Composition relationship

Generalization

Figure 9:

Example of

Generalization

relationship

cont..Generalization

Generalization is another name for inheritance or an "is a" relationship.

It refers to a relationship between two classes where one class is a

specialized version of another.

To model generalization on a class diagram, a solid line is drawn from the

child class (the class inheriting the behavior) with a closed, unfilled

arrowhead (or triangle) pointing to the super class .

For example, Corporate Customer and Personal Customer are types of

Customer. So the classes Corporate Customer and Personal Customer

would have a generalization relationship with the class Customer.

The children classes inherit the attributes and operations of the parent

class.

Example of a Class Diagram

Figure 10: Example of a Class Diagram

Example of a Class Diagram in EA