• The waterfall model was introduced by Winston Royce in 1970.
  • The waterfall model is the simplest software process model. It is a traditional or modest model.
  • It is the simplest SDLC model which is mostly used for small projects.
  • In the waterfall model, all development activities are divided into various phases.
  • The phase is organized in a linear order. That's why it is also called a linear model.
  • In the waterfall model, the output of one phase is used as the input to the next phase.
  • Each phase begins after the previous phase has finished.
  • Each phase has well-defined starting and ending points.
  • The output of the phase is used as the input of the next phase that's why it is also called a sequential model. 
  • Various phases of the waterfall model are performed one after the other and fall like water falling from the sky that's why it is called the waterfall model.

The phase/step of the Waterfall model are:- 

1. Requirement gathering 2.Analysis 3. Design 4.Coding 5. Testing 6. Maintenance





1.  Requirement gathering:- It is the first phase/step of the waterfall model. It the most important step in the waterfall model. And in this, the developer and the customer do a meeting for discussing the requirement of the customer. Or we can say that in this step of the waterfall model customer tell about its requirement regarding the project or software.  

 2.  Analysis:- It is the second step of the waterfall model. This is also a very important phase/step of the waterfall model. The "analysis" is done after the "requirement gathering". In this step of the waterfall model, the developer collects all the information related to the project/software. Or we can say collect all the information which helps to full-fill the needs of the customer. 

3.  Design:- It is the third phase/step of the waterfall model. It is also a very important phase/step of the waterfall model. This step of the waterfall model is done after the step of the "Analysis". In this phase/step of the waterfall model, the developer makes a layout of the software or project which is called SRS. SRS is written documentation of all information about the software. The SRS is a very important document because it is written in the project/software.

 4.  Coding:- It is the fourth phase or step of the waterfall model. It is also a very important phase/step of the waterfall model. This phase/step of the waterfall model is done after the "design" step of the waterfall model. Form this phase/step of coding the actual programming or coding is started. In this phase/step of the waterfall model, the developer starts programming to take SRS as an input. 

5.  Testing:-  It is the fifth phase/step of the waterfall model. It is also a very important phase/step of the waterfall model. This phase/step of the waterfall model is done after the "coding" phase/step of the waterfall model. In this step of the waterfall model, the developer checks or test the project/software that it is working or not, the developer also check that each and every requirement of the customer is done or not. In this step of the waterfall model, the developer makes sure there is no error in the projector software.

6.  Maintenance:- It is the sixth step/phase of the waterfall model. And it is the last phase/step of the waterfall model. It is also a very important phase or step of the waterfall model. Maintenance is the phase/step to enhance the product some better versions are released. Maintenance is done to deliver these changes in the customer environment. Maintenance, phase/step is used to update the project/software.


ADVANTAGES OF THE WATERFALL MODEL:-


  • It is a linear model.
  • It is the simplest model in the SDLC model.
  • It is easy to explain to the user.
  • Widely used.
  • Easy to arrange tasks.
  • Works well for smaller projects where requirements are very well understood.
  • Phases are processed and completed one at a time.
  • Stages and activities are well-defined.

DISADVANTAGE OF THE WATERFALL MODEL:-

  • Disallows changes.
  • Cycle time too long.
  • User feedback not allowed.
  • We can not go in the backward direction while SDLC performs.
  • It is difficult to define all requirements at the beginning of the project.
  • High amounts of risk and uncertainty.
  • Not a good model for complex and object-oriented projects.
  • Poor model for long and ongoing projects.