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Waterfall Model In Software Engineering



waterfall model in software engineering with an example

WATERFALL MODEL in software engineering is also known as a sequential model or traditional model or basic model. It is a step by step procedure to develop new software“.  In the waterfall model, requirement changes were not allowed and the next phase is started only when the desired set of the goal is achieved from the previous phase.

It is known as the first model approached in SDLC. It was introduced in 1970 by Winston Royce

Why the model is called a waterfall model?

Here backtracking is not possible. It means once after the feasibility study is completed, the requirement is freezed. You cannot go back and take up the requirement changes. So, this model is called a waterfall model.

And also all these phases are cascaded to each other in which progress seems as flowing steadily downwards (like a waterfall) through the phases.

7 phases of Waterfall Model

There are 7 phases of the waterfall model. Almost all the SDLC models have the same phases or stages. The difference is present in its process of execution. 

stages of waterfall model

The seven phases of the waterfall model in software engineering are given below:

  1. Requirement collection

    Requirement collection is the first stage for any software development process. It is done by the Business Analyst.

    The business analyst will go to the customer’s place and ask for the requirement. The customer will give the requirement in business language. Now
    the business analyst will convert those requirements in the software language which can be understood by team members in the company.

    Sometimes even Product Analyst collects the requirements. Product Analyst is the term used in product based companies.
    Product Analyst will do market research and collects information from the customers. And that information collected is taken as the input or requirement in order to develop a new product.

  2. Feasibility study

    This is the second phase of the waterfall model is a feasibility study. And this is actually an analysis phase. Once after the requirement is collected, then it is analyzed properly, so the company can make a further decision regarding the project. It is basically done by the team members. Business analyst, project manager, architects, finance team and HR team are basically involved in doing a feasibility study.

    In this phase, they will decide, whether they can practically implement the project or not. Do they have required lab setup or not. Even if they take up the project, will they make a profit or not? What can be obstacles and problems while implementing this project in the future? So, in this way, the team members will analyze the various factors before actually implementing the project.

  3. Design

    The third phase of the waterfall model in software engineering is the design. And it is done by the architects. Architects will always think from a technical point of view. And they will develop design according to the requirement. They will do a high-level and low-level design.

  4. Coding

    Once when the design is completed, it is given to the developers. Now the developers will write the programs or codes by looking into the low-level design.

    If the developers get any problem with the design or requirement they will communicate with the team members or business analyst or project manager. Once after coding is completed, developers will do White Box Testing

  5. Testing

    Once when the software is developed, the developers will give the software to the software testing engineers. Now the test engineers will test the software by executing the test cases.

  6. Installation

    Finally, when the testing is complete and the quality of the software is good, then the product is ready for the installation.

    The site engineer or installation engineer or the field engineer from the company will travel to the customer’s place in order to install the software in the production server.
    Firstly, the site engineer will set up the environment for the installation of software. And finally, he will install the software.

    Once after the installation is successful, the customer can use the software and run his business.

  7. Maintenance

    This is the last phase in the software development life cycle of the waterfall model. So, once when the customer is using the software and supposes while using, a bug is found. So now what to do?

    Actually, the company will always provide support to the customer for a certain period of time. This period of time is known as the maintenance period. The maintenance period is according to the agreement signed between the customer and the company.

    Let’s say the maintenance period is for 6 months, so till that 6 months, the company will provide full support to the customer and will fix all the defects. In simple words, it is just like a warranty period. And once when the warranty period is over, the company will charge for fixing any defects or problem in the software. The maintenance phase is also known as ‘Mute Phase’ because there is no implementation or any action going on in this phase. 

When to use waterfall model in software engineering?

When the projects match the given conditions, then you can go for the waterfall model:

  • When customers give requirement and he will tell he will not change the requirement.
  • For short term and simple projects.
  • Technology and tools to be used are available and stable.
  • When the project is not too big and complicated.
  • When a resource is available and sufficient.
  • The requirement is clear.

What happens if the requirement is changed in the waterfall model?

When there is a change in the requirement, all the different phases will change as shown in the diagram below.

requirement changes in waterfall model in software engineering

Firstly, when the requirement collection changes,  it will cause a change in the feasibility study phase and even designs will change. And when the design changes, the coding should be changed, according to the design. And finally, this leads to generating a lot of defect in the testing phase.

So, because of this, you may not release quality software to the customer in the given time. Moreover, the cost of fixing the defect will be more and this may lead to losses.

Disadvantages of waterfall model in software engineering

  • Requirement changes are not allowed.
  • Since this is the first model introduced for the development process, during those days’ developers were involved in the testing process and this was one of the big disadvantages. 
  • The total investment is more because the cost of fixing the defect is more.
  • If there is a defect in the requirement, it will flow till the end of the development and this leads to a lot of pre-working and time-consuming.
  • Requirement collection and design is not tested.
  • Waterfall model is not a flexible model to adopt.
  • Customers should wait for a long period just to see the software (i.e. the process is slow)

Advantages of waterfall model in software engineering

  • Since the requirement is not changed, in testing phase number of a defect will be less.
  • Product quality obtained is good.
  • It is very simple to model to adopt.
  • Developers have to do less recoding so this is advantages of for them
  • The initial investment is less because, in this model, the testing team is hired once when the coding completes.


Waterfall model is the basic model which was firstly introduced in the software development process. The company follows this model for small and short term projects. And the most important drawback of the waterfall model is that requirements are not changed. And this is not a flexible model to work on for complex projects. So mostly agile model is used for long term projects.

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