Design Methodologies: Structured and Object-Oriented Design

Design Methodology

(Structured Design and Object-Oriented Design)

Introduction to Design Methodology

Design methodology refers to the systematic approach used to create the structure and organization of a software system. It defines how design activities are carried out and how system components are organized.

After understanding design fundamentals, the next step is deciding how to design. This is where design methodologies come into play.

There are two major design methodologies:

Structured Design
Object-Oriented Design (OOD)

Each methodology has its own principles, techniques, advantages, and suitable application areas.

2️. Structured Design

2.1 Introduction to Structured Design

Structured Design is a traditional software design methodology that focuses on functions and processes. It is derived from structured analysis and is mainly used in procedural programming.

The main objective of structured design is to divide the system into smaller functional modules using a top-down approach.

In this approach, the system is decomposed step-by-step into smaller and manageable modules.

2.2 Key Concepts of Structured Design

🔹 Top-Down Decomposition

The system is first viewed as a whole and then broken down into smaller sub-systems and modules. Each module performs a specific function.

This makes the system easier to understand and implement.

🔹 Functional Decomposition

The entire system is divided into smaller functional units. Each function is clearly defined and implemented separately.

This helps reduce complexity and improves maintainability.

🔹 Structure Charts

Structure charts are graphical tools used in structured design. They show:

Module hierarchy
Module interactions
Data flow between modules

Structure charts help visualize the system structure clearly.

🔹 Cohesion and Coupling

Structured design emphasizes:

High cohesion (modules perform single task)
Low coupling (minimal interdependence between modules)

These principles improve system quality.

2.3 Advantages of Structured Design

Easy to understand
Suitable for small and medium projects
Clear modular representation
Works well with procedural languages like C

2.4 Limitations of Structured Design

Not suitable for very large systems
Difficult to handle changing requirements
Focuses more on functions than real-world entities
Limited reusability

3. Object-Oriented Design (OOD)

3.1 Introduction to Object-Oriented Design

Object-Oriented Design is a modern design methodology that focuses on objects instead of functions.

An object represents a real-world entity and contains:

Attributes (data)
Methods (behavior)

OOD is based on Object-Oriented Programming principles such as:

Encapsulation
Inheritance
Polymorphism
Abstraction

It is widely used in modern software development.

3.2 Key Concepts of Object-Oriented Design

🔹 Objects and Classes

A class is a blueprint, and objects are instances of that class.

For example:
Class: Student
Object: Rahul (instance of Student)

This makes modeling real-world systems easier.

🔹 Encapsulation

Encapsulation binds data and methods together and hides internal details from outside access.

It increases security and reduces system dependency.

🔹 Inheritance

Inheritance allows one class to acquire properties of another class.

This supports reusability and reduces redundancy.

🔹 Polymorphism

Polymorphism allows objects to behave differently under different conditions.

It improves flexibility and scalability.

🔹 UML Diagrams

Object-Oriented Design commonly uses UML diagrams such as:

Class diagrams
Sequence diagrams
Use case diagrams
Activity diagrams

These diagrams visually represent system structure and behavior.

3.3 Advantages of Object-Oriented Design

High reusability
Better scalability
Easy maintenance
Real-world modeling
Suitable for complex systems

3.4 Limitations of Object-Oriented Design

Requires understanding of OOP concepts
More complex than structured design
Initial design may take more time

4️⃣ Comparison: Structured Design vs Object-Oriented Design

Aspect	Structured Design	Object-Oriented Design
Focus	Functions	Objects
Approach	Top-down	Bottom-up
Programming Style	Procedural	Object-Oriented
Reusability	Low	High
Maintenance	Difficult	Easier
Suitable For	Small systems	Large & complex systems

5️⃣ When to Use Which Methodology?

Structured Design is suitable when:

Requirements are stable
System is small
Procedural programming is used

Object-Oriented Design is suitable when:

System is complex
Long-term maintenance is required
Reusability is important
OOP languages are used

📌 Conclusion

Design methodology defines how software structure is created. Structured Design focuses on functional decomposition using a top-down approach, while Object-Oriented Design focuses on modeling real-world objects using classes and inheritance.

In modern software development, Object-Oriented Design is widely preferred because of its flexibility, reusability, and scalability. However, structured design remains useful for smaller procedural systems.

Understanding both methodologies enables software engineers to choose the appropriate design approach based on project requirements.