Different types of SDLC Model (Waterfall, Prototype, Agile and spiral model)

Waterfall Model

The Waterfall Model is one of the oldest and simplest Software Development Life Cycle (SDLC) models. In this model, software is developed phase by phase in a fixed sequence. Each phase must be completed before moving to the next phase. Once a phase is finished, it is difficult to go back and make changes.

Waterfall Model is a linear and sequential software development model in which each phase is completed before moving to the next phase.

When to Use the Waterfall Model

Use the Waterfall Model when:

Requirements are clear and fixed.
The project is small or medium-sized.
Technology is well understood.
Customer involvement is limited after requirements are collected.
Changes during development are very unlikely.
Proper documentation is required.

Examples

Payroll Management System
Library Management System
School Management System
Government Projects
Inventory Management System

Phases of the Waterfall Model

The Waterfall Model consists of 6 phases, which are completed one after another.

1. Requirement Gathering and Analysis

Explanation

Meet with the customer.
Collect all project requirements.
Analyze the feasibility of the project.
Prepare the Software Requirement Specification (SRS).

Output: SRS (Software Requirement Specification)

2. System Design

Explanation

Design the overall structure of the software.
Prepare database design, user interface, and system architecture.
Decide how the software will work.

Output: System Design Document

3. Implementation (Coding)

Explanation

Developers write the program based on the design.
Each module is developed according to the requirements.

Output: Source Code

4. Testing

Explanation

Test the completed software.
Find and fix errors (bugs).
Verify that the software meets the requirements.

Output: Tested Software

5. Deployment

Explanation

Install the software on the customer's system.
Deliver the software for actual use.

Output: Working Software

6. Maintenance

Explanation

Fix bugs found after deployment.
Update the software.
Add small improvements if necessary.

Output: Updated Software

Important: In the Waterfall Model, the next phase begins only after the previous phase is completed.

Advantages and Disadvantages of the Waterfall Model

S.N.	Advantages	Disadvantages
1	Simple and Easy to Understand – The model is easy to learn and follow.	Difficult to Change Requirements – Changes are hard to make once a phase is completed.
2	Well-Structured Process – Each phase is completed before moving to the next.	Late Testing – Testing is performed only after the development phase.
3	Easy to Manage – Clear milestones and documentation make project management easier.	Limited Customer Involvement – Customers usually provide feedback only at the beginning and end.
4	Good Documentation – Every phase is properly documented for future reference.	Higher Risk – Errors found late can be expensive to fix.
5	Suitable for Small and Fixed Projects – Works well when requirements are clear and stable.	Working Software is Delivered Late – The customer gets the final product only after all phases are completed.
6	Easy Progress Tracking – Progress is easy to monitor because phases are clearly defined.	Not Suitable for Large or Changing Projects – It is not flexible enough for projects with changing requirements.

Features of the Waterfall Model

Linear and sequential development
Each phase is completed before the next begins
Requirements are fixed at the beginning
Well-defined documentation
Easy to understand and manage
Testing is performed after coding
Less customer involvement during development

Prototype Model

The Prototype Model is a software development model in which a working sample (prototype) of the software is created before developing the final product. The customer reviews the prototype, provides feedback, and the prototype is improved until the requirements are clear. After the requirements are finalized, the actual software is developed.

Prototype Model is a software development model in which a prototype (working model) is developed first to understand customer requirements before building the final software.

When to Use the Prototype Model

Use the Prototype Model when:

Requirements are not clear or are incomplete.
The customer is not sure about the final product.
Frequent customer feedback is required.
The project involves a new system or technology.
User interface (UI) design is important.
Changes in requirements are expected during development.

Examples

ATM System
Online Shopping Website
Hospital Management System
Mobile Applications
Online Banking System

Phases of the Prototype Model

The Prototype Model consists of 6 phases.

1. Requirement Gathering

Meet with the customer.
Collect the initial requirements.
Identify the basic features of the software.

Output: Initial Requirements

2. Quick Design

Prepare a simple design of the software.
Focus mainly on the user interface (UI) and important functions.

Output: Basic Design

3. Build a Prototype

Develop a working prototype (sample model).
The prototype shows how the software will look and work.

Output: Prototype

4. Customer Evaluation

Explanation

The customer reviews and tests the prototype.
Feedback and suggestions are collected.
Missing or incorrect requirements are identified.

Output: Customer Feedback

5. Refine the Prototype

Explanation

Improve the prototype based on customer feedback.
Repeat the design, development, and evaluation process until the customer is satisfied.

Output: Approved Prototype

6. Engineering Product (Develop the Final System)

Build the complete software using the approved prototype as a guide.
Test and deploy the final software.

Output: Final Software

Fig follow from website

Important: The prototype is repeated and improved until the customer approves it. Only then is the final software developed.

Advantages and Disadvantages of the Prototype Model

S.N.	Advantages	Disadvantages
1	Clear Requirements – Helps customers understand and refine their requirements.	Time-Consuming – Building multiple prototypes takes extra time.
2	Customer Involvement – Customers provide continuous feedback during development.	Expensive – Developing and modifying prototypes increases the cost.
3	Early Error Detection – Problems are identified before the final system is developed.	Scope Creep – Frequent changes may increase the project scope.
4	Improved Software Quality – Continuous feedback results in a better final product.	Customer Confusion – Customers may think the prototype is the final product.
5	Reduced Development Risk – Unclear requirements are resolved early.	Poor Documentation – More focus is placed on the prototype than on documentation.
6	Higher Customer Satisfaction – The final product closely matches customer needs.	Not Suitable for Large Projects – Managing prototypes for very large systems can be difficult.

Features of the Prototype Model

A working prototype is created before the final system.
Continuous customer involvement and feedback.
Easy to modify requirements.
Requirements become clear before final development.
Repeated improvement of the prototype.
Better communication between developers and customers.
Suitable for systems with unclear requirements.

Agile Model

Agile Model is a software development model in which the project is developed step by step (in small parts called iterations or sprints). The customer gives feedback after each iteration, and changes can be made at any stage.

Agile Model is a software development model that develops software in small, incremental parts with continuous customer feedback and frequent improvements.

When to Use the Agile Model

Use the Agile Model when:

Requirements change frequently.
Customer involvement is available throughout the project.
Quick delivery of working software is needed.
Large projects can be divided into small modules.
The project needs continuous testing and improvement.
The development team works closely together.

Examples

Mobile App Development
E-commerce Websites
Banking Applications
Online Learning Systems
Social Media Applications

Phases of Agile Model

Unlike the Waterfall model, Agile repeats these phases in every iteration (Sprint).

1. Requirement Gathering (Planning)

Explanation

Discuss project requirements with the customer.
Prioritize important features.
Plan the work for the next sprint.

Output: Product Backlog (List of features)

2. Design

Explanation

Prepare the system design.
Design database, interface, and architecture for selected features.

Output: Design documents

3. Development (Coding)

Explanation

Developers write the program.
Only the selected features for that sprint are developed.

Output: Working software module

4. Testing

Explanation

Test the developed module.
Find and fix bugs.
Ensure the software works correctly.

Output: Tested software

5. Deployment (Release)

Explanation

Deliver the working software to the customer.
Customer starts using the new features.

Output: Software release

6. Review and Feedback

Explanation

Customer reviews the software.
Gives suggestions and feedback.
Improvements are planned for the next sprint.

Output: Updated requirements

Advantages of Agile Model

S.N.	Advantage	Explanation
1	Flexible	Easy to change requirements during development.
2	Customer Satisfaction	Customer gives feedback regularly.
3	Faster Delivery	Working software is delivered quickly.
4	Better Quality	Continuous testing improves quality.
5	Reduced Risk	Problems are identified early.
6	Better Communication	Developers and customers work closely together.
7	Easy Bug Fixing	Bugs are found and fixed in every sprint.

Disadvantages of Agile Model

S.N.	Disadvantage	Explanation
1	Requires Customer Involvement	Customer must participate regularly.
2	Difficult Cost Estimation	Total cost may change as requirements change.
3	Scope Creep	Continuous changes may increase project scope.
4	Needs Experienced Team	Developers must be skilled and collaborative.
5	Documentation May Be Limited	Focus is more on working software than extensive documentation.
6	Not Suitable for Small Fixed Projects	If requirements are already fixed, Waterfall may be better.

Features of Agile Model

Incremental development
Iterative process
Customer involvement
Continuous testing
Frequent software releases
Flexible to changing requirements
Team collaboration
Fast delivery

Real-Life Example

Suppose a company wants to develop an Online Shopping App.

Sprint 1

User Registration
Login
Home Page

➡️ Delivered to customer for feedback.

Sprint 2

Product Search
Product Details
Shopping Cart

➡️ Customer reviews and suggests improvements.

Sprint 3

Payment System
Order Tracking
Notifications

➡️ Final product becomes ready through multiple small releases.

Agile vs Waterfall (Quick Comparison)

Feature	Agile	Waterfall
Development	Incremental (small parts)	Sequential (one phase at a time)
Requirement Changes	Easy	Difficult
Customer Involvement	High	Low
Testing	Continuous	At the end
Delivery	Frequent	Once after completion
Flexibility	High	Low

Exam Points (2–5 Marks)

Spiral Model

The Spiral Model is a software development model that combines the features of the Waterfall Model and Prototype Model. It develops software through repeated cycles called spirals, with a strong focus on risk analysis in every cycle.

Spiral Model is a software development model that develops software in repeated cycles (spirals), where risk analysis is performed before each development phase.

When to Use the Spiral Model

Use the Spiral Model when:

The project is large and complex.
The project has high risk.
Requirements may change during development.
The project uses new or advanced technology.
Customers want regular feedback and improvements.
The project is expensive and failure would be costly.

Examples

Banking Systems
Air Traffic Control Systems
Defense and Military Software
Space Research Software
Large Healthcare Systems

Phases of the Spiral Model

Each spiral (cycle) consists of 4 phases.

1. Planning (Objective Setting)

Explanation

Identify project objectives.
Gather customer requirements.
Plan the activities for the next cycle.

Output: Project plan

2. Risk Analysis

Explanation

Identify possible risks.
Analyze technical, financial, and schedule risks.
Develop solutions to reduce or remove risks.

Output: Risk management plan

3. Engineering (Development and Testing)

Explanation

Design the software.
Write the code.
Test the developed module.
Fix errors.

Output: Working software module

4. Evaluation (Customer Review)

Explanation

Deliver the developed module to the customer.
Customer reviews the software.
Feedback is collected.
Plan the next spiral if needed.

Output: Customer feedback

Advantages of the Spiral Model

S.N.	Advantage	Explanation
1	Better Risk Management	Risks are identified and reduced early.
2	Flexible	Changes can be made in every spiral.
3	Customer Feedback	Customer reviews every cycle.
4	High Quality	Testing is done in every iteration.
5	Suitable for Large Projects	Works well for complex and high-risk projects.
6	Early Error Detection	Problems are found and fixed early.

Disadvantages of the Spiral Model

S.N.	Disadvantage	Explanation
1	Expensive	Risk analysis increases the cost.
2	Complex	Difficult to manage and understand.
3	Requires Risk Experts	Skilled professionals are needed to analyze risks.
4	Time-Consuming	Multiple cycles increase development time.
5	Not Suitable for Small Projects	Too costly and complex for simple projects.

Features of the Spiral Model

Risk-driven development
Iterative (repeated cycles)
Customer feedback after each cycle
Continuous testing
Flexible to changing requirements
Suitable for large and high-risk projects

Real-Life Example

Suppose a bank wants to develop an Online Banking System.

Spiral 1

Plan basic features
Analyze security risks
Develop login system
Customer reviews it

Spiral 2

Add money transfer
Analyze transaction risks
Develop and test transfer module
Customer reviews it

Spiral 3

Add bill payment
Analyze payment risks
Develop and test payment system
Customer reviews it

The process continues until the complete banking system is ready.

Spiral Model vs Prototype Model

Feature	Spiral Model	Prototype Model
Main Focus	Risk Analysis	Requirement Clarification
Development	Iterative with risk analysis	Prototype creation and refinement
Customer Feedback	After every spiral	After every prototype
Best For	Large, complex, high-risk projects	Projects with unclear requirements
Cost	High	Medium

Different types of SDLC Model (Waterfall, Prototype, Agile and spiral model)

Waterfall Model

Prototype Model

Agile Model

Spiral Model

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