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278 Part 3 • the analysis Process

Figure 10.19 Student Campus Organization
An example of whole/part and –studentNumber –organizationNumber
aggregation relationships. –creditsCompleted –organizationName
–gradePointAverage –organizationType
–department –president
–major –treasurer
–minor –secretary
+changeStudent( ) –accountBalance
+findStudent( ) –numberOfMembers
+graduateStudent( ) +change( )
+initialize( ) +changeOfficers( )
+studentComplete( ) +new( )
+viewStudent( )

Fund Raising Activity
–activityNumber
–activityDescription
–activityType
–amountSpent
–amountReceived
–dateCompleted
+change( )
+new( )
+recordAmount( )

Generalization/Specialization (Gen/Spec) Diagrams
A generalization/specialization (gen/spec) diagram may be considered to be an enhanced class
diagram. Sometimes it is necessary to separate the generalizations from the specific instances.
As we mentioned at the beginning of this chapter, a koala bear is part of a class of marsupials,
which is part of a class of animals. Sometimes we need to distinguish whether a koala bear is an
animal or a koala bear is a type of animal. Furthermore, a koala bear can be a stuffed toy animal.
We often need to clarify these subtleties.
GEnEralization. A generalization describes a relationship between a general kind of thing
and a more specific kind of thing. This type of relationship is often described as an “is a”
relationship. For example, a car is a vehicle and a truck is a vehicle. In this case, vehicle is the
general thing, whereas car and truck are the more specific things. Generalization relationships
are used for modeling class inheritance and specialization. A general class is sometimes called
a superclass, base class, or parent class; a specialized class is called a subclass, derived class,
or child class.

inhEritanCE. Several classes may have the same attributes and/or methods. When this occurs,
a general class is created, containing the common attributes and methods. The specialized class
inherits or receives the attributes and methods of the general class. In addition, the specialized
class has attributes and methods that are unique and only defined in the specialized class. Creating
generalized classes and allowing the specialized class to inherit the attributes and methods helps to
foster reuse because the code is used many times. It also helps to maintain existing program code.
This allows the analyst to define attributes and methods once but use them many times, in each
inherited class.
One of the special features of the object-oriented approach is the creation and maintenance
of large class libraries that are available in multiple languages. So, for instance, a programmer
using Java, .NET, or C# will have access to a huge number of classes that have already been
developed.

PolymorPhism. Polymorphism (meaning “many forms”), or method overriding (not the same
as method overloading), is the capability of an object-oriented program to have several versions