Object-Oriented Design vs Functional Decomposition

Object-Oriented Design vs Functional Decomposition

A Look at Two Software Design Methodologies

Importance of software design in software development lifecycle

Design is a crucial aspect of the software development process that enables developers to create effective and efficient solutions to real-world problems. Essentially, design involves creating a blueprint or plan for the software system that needs to be developed, which outlines what needs to be done, how it will be accomplished, and the resources required for the task.

Proper design is essential for creating software that satisfies the requirements of users and stakeholders, can be maintained, and can be extended or modified as needed. Without adequate design, software systems are prone to errors, delays, and costly rework. I’ve experienced this firsthand in one of my previous projects, where we rushed into the development phase without adequate design, causing significant delays and numerous iterations.

When developers invest time in designing a software system, they can ensure that it is scalable, reliable, and efficient, making it easier to understand, test, and debug. Ultimately, a well-designed software system can help reduce overall development time and costs while improving the quality of the final product.

Object-oriented design

The steps involved in object-oriented design are as follows:

  1. Identify the problem to be solved

  2. Identify the objects in the system

  3. Define the relationships between objects

  4. Define the interface for each object

  5. Document the design

Sample Object Oriented design of Library Management System.

Library Management System OO Design

Functional Decomposition Design

Functional decomposition is a design technique that helps developers to create a large and complex system by breaking it down into smaller, more manageable pieces or functions. The process involves analyzing the system and identifying the key functions that it performs. These functions are then organized into a hierarchical structure, where each function can be further broken down into smaller functions until they are simple enough to be implemented as code. This approach helps developers to understand and manage the system’s complexity by focusing on individual components and their interactions, rather than the system as a whole. By breaking down the system into smaller functions, developers can develop and test each component independently, which can help to ensure that the final product works as intended.

Steps to do functional Decomposition

  1. Identify the system or process to be decomposed

  2. Identify the high-level functions of the system

  3. Decompose each high-level function into more detailed sub-functions

  4. Repeat the decomposition process for each sub-function

  5. Define the interfaces between functions

  6. Document the functional decomposition

Sample Functional Decomposition of Library Management system

Sample Design Library Management System using functional Decomposition


Functional decomposition is a design methodology where the system is broken down into smaller functions or modules, each responsible for performing a specific task. These functions can be independent or dependent on each other. An example of this approach is a program that calculates the sum of two numbers by calling a function.

Object-oriented design is a methodology where the system is divided into objects that represent entities or concepts with properties and behaviors. The objects contain data and their associated methods. These objects can be dependent on each other through inheritance or composition. An example of this approach is a program that represents a bank account object with methods like deposit, withdraw, and check balance.

Both functional decomposition and object-oriented design have their strengths and weaknesses. Functional decomposition is good for creating small, reusable functions. Object-oriented design, on the other hand, is good for modeling complex systems with multiple objects and interactions. Developers can choose the approach that suits their specific requirements and project goals.

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