VBM - Vision Based Methodology™

Activity 7: Creating the Vision

A look at Object Oriented Design

In design, close attention is paid to the external view of each class (messages, parameters, public data, and public processes) and the internal view (private data and private processes).

OO Design Approach:

1. Design the physical Classes and specify the physical data elements, processes, and rules which will be a part of each Class.
2. Design the Screen (Window) layout associated with each Class or group of Classes.
3. Identify the Navigation through the classes based on the identified States and Business Events.
4. Identify the matching navigation through the related screens (windows).
5. Examine existing class libraries for candidate reuse sub-classes.
6. Identify sub-classes which can be reused by both higher level batch and on-line Class processes.
7. Create an OO Structure Chart for each physical Class.
8. Define the logic for each individual Class process.
9. Perform Class generalization where appropriate to insure that reasonable reusablity exists.

Suggested Models:

• Class Navigation Diagram
• OO Structure Chart

Important OO Concepts:

Class Library

A pre-written, pre-tested library of reusable classes (modules) which can be inherited (utilized) by multiple programs which are developed within the common framework.

Encapsulation

The data and the processes or functions (program code) which manipulate the data are encapsulated into stand alone object called a class.

Inheritance

A higher level class can contain other lower level classes. In this situation, the higher level derived class inherits and utilizes all of the data and processing (program code) contained in the lower level objects (parent classes). General functions in parent class, custom functions in the sub-classes.

Polymorphism

An operator or function can perform one way when used within one class but perform differently when used by another class. The system builder defines these multiple behaviors based on the requirements of the object. This allows the objects (classes) to be reused with operational changes without rewriting the program code.This makes inheritance possibilities more flexible.

OO Tips:

• Don't recreate the wheel! Find existing general purpose classes first. Commercial libraries or books.
• Evolve classes from specific purpose to general purpose.
• Document the Class!

Objected Oriented Design encourages disciplined and forward focused planning as each new class (module) is created. Care should be taken on the part of the designer to insure a high level of reusability. The advantage is not just the elimination of redundant data but also the elimination of redundant processes.