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OOAD & UML - Part 3. Identifying Classes - Class Diagram

The class diagram is the main building block in object oriented modeling. They are being used both for general conceptual modeling of the systematics of the application, and for detailed modeling translating the models into programming code. The classes in a class diagram represent both the main objects and or interactions in the application and the objects to be programmed.

Identify classes from the use cases and sequence diagrams. Following are the 3 classifications of classes.

1. User Service Classes (Form level objects)
2. Business Service Classes (Control level objects)
3. Data Service Classes (Entity level objects)

Below are some techniques for identifying classes. The first level is called as Analysis level classes.

1. 3 classes for each use case,
2. 1 class each for external actors,
3. 1 class each for alternate & exception flows.

Now after these, we have to exclude classes on following rules...

1. Exclude classes which don't have functionality
2. Exclude classes which do repetitive job
Now after following above rules, we will be left with following classes.


Actors-
ProfessorRegistrar
Student-


User Service Classes-
AuthenticationCancel Registration
Maintain Course DetailsMaintain Professor Details
Maintain Student DetailsModify Schedule
NotificationRecord Grades
RegistrationRegistration for Secondary Courses
Sign up to TeachView Report Card
View Student Details-


Business Service Classes-
Cancel RegistrationExceptions
Maintain Course DetailsMaintain Professor Details
Maintain Student DetailsModify Schedule
NotificationRecord Grades
RegistrationAuthentication
Sign up to Teach-


Data Service Classes-
AuthenticationMaintain Course Details
Maintain Professor DetailsMaintain Student Details
Record GradesRegistration
Sign up to Teach-

Packages which store classes

 
Class diagram

Likewise classes need to be defined for all the classes identified (depicted in the class package).

Here in this series on OOAD and UML, I have tried to give some simple tips and tricks for identifying use cases, preparing sequence diagrams and identifying classes. Hope you have liked the series. If you have any doubts on the process, please feel free to post a comment...

This series includes 3 parts...
Part 1. Identifying Use Cases – Use Case Diagrams
Part 2. Realizing Use Cases – Sequence Diagrams
Part 3. Identifying Classes – Class Diagrams


- Vighnesh Bendre 
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