Introduction to Waterfall Model

The waterfall model is one of the earliest models of software development in which tasks are executed sequentially, starting from the top with feasibility and flowing down through various tasks with implementation into the live environment. Requirements flow into the design, which flows into building or implementation, and finally into tests. As the testing process occurs at the end of the model, getting feeds passed back up the waterfall has been challenging.

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To work on the waterfall model, we need to understand its application approach based on both internal and external factors, which can be as follows:

No ambiguous requirements in the application.
Stability of product definition.
It is technology understood.
It is not dynamic.
Large resources with appropriate expertise are available to support the product.
Very short length project.
The good document, clear and fixed requirements.

To start with the history of the waterfall model, I would like to say that the first sample of the waterfall model was introduced in the year 1970 by Winston w Royce in an article. Since then, the waterfall model state that one should switch to another phase only when the previous phases are completely tested, reviewed, and verified. It emphasizes the logical progression of phase steps. Its functionality is similar to the water flowing over the edge of a cliff.

This software development approach has been named waterfall because it develops systematically from one phase to another in a downward fashion. Since the time it was first published by Winston W. Royce in 1970, the waterfall model has been used widely in the field of software development. In the software development process cycle, programming models are used to plan the various stages of developing an application. One such model is the waterfall model.

Phases of Waterfall Model

Given below are the phases of waterfall model:

With the above infographics, we can understand that the waterfall model has a total of 7 phases of the design and development software cycle which are as follows:

Requirements
Analysis
Design
Coding / Implementation
Testing
Operation / Deployment
Maintenance

So we can see that the waterfall model works hierarchy from top to bottom, with one phase completed with full verifications and then switching to another phase, including phase processes like Conception, Initiation, Analysis, Design, Construction, Testing, Production/Implementation, and Maintenance. To get a more brief knowledge about the waterfall model, we need to understand its processes deeply with its work model. A primary prerequisite phase needs to be understood before starting the deep phases of knowledge. It is about the feasibility study for the software product. It deals with the financial and technical aspects of the project requirements. This phase deals with correcting the measures based on the analyzed benefits and drawbacks. Thus the best solution is chosen.

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1. Requirements

Specifically, we need to know and understand what we have to design, what we have to develop, its processes, what will be its functionality, etc. It provides input material to the product being made; thus, the upcoming product is studied, finalized, and marked. It also gives us the extension to decide the hardware or software requirements of the product which will be designed, developed, and captured in all phases.

2. Analysis

It results in designing models, schema, and business rules.

Not only this requirement is divided into two parts:

Requirement gathering and analysis: First, all the information and requirement for the product development is gathered from the customer and processed for analysis. The primary role of this part is to eradicate incompleteness and inconsistencies related to software product development.
Requirement specification: Then, the above-analyzed requirements are documented in an SRS (software requirement specification ) document. It serves as a path between the customer and the SRS development team. Any disputes in the future are managed and settled through this SRS documentation only.

3. Design

After the first phase is completed and verified, it is the next most important phase to be studied as it is used for system design. It helps in specifying software and hardware requirements for the product design. It also helps in the overall architecture of the system design. So the requirement specification is mainly studied and verified in this phase. It is also helpful in transforming the SRS document into functional design and development of the software product. So we can say that in the designing phase, one makes the overall architecture for the software development project.

4. Implementation

With system design fully verified, the implementation phase comes in a row. In this phase, the inputs from system design are taken, and it is first developed in small programs known as units, which are tested and implemented in the upcoming phase. Each unit in the implementation phase undergoes development, and its full functionality is tested, also known as unit testing. So in this phase, the system design is converted into source code with fully functional program modules. It includes the development, proving, and integration of the software.

5. Integration and Testing

Each unit design and development in the earlier phases are incorporated from the implementation phase, which is integrated into a module or system for various tests like load test, load test, etc., after testing each unit. The testing environment undergoes a constant software check to determine if there is any flow or error in the design or code. Testing is done to maintain the stability and feasibility of the software so that the client does not face any disturbances or bugs during its production. So in this phase, the whole system is tested thoroughly for any faults and failures after implementation.

System testing consists of three different types of activities which can be given below:

Alpha (α) Testing: The testing done by the development team.
Beta (β) Testing: It is the testing done by a friendly team of customers and users.
Acceptance Testing: It is done after the alpha testing and beta testing. It’s done after delivery by the customers. After the customer performs testing, the decision is taken whether this software is acceptable or rejected. So in this phase, debugging bugs is done.

6. Deployment of the System / Operations

Once the non-functional, functional, alpha, and beta testing are done, the software product is deployed to the user or customer system or released to the market. The deployment phase includes installation, migration, and support of the complete system to the user or customer environment.

7. Maintenance

It is the last but the most important phase in the waterfall workflow model. This step comes just after installation, and it includes making the appropriate modification to the product or system or enhancing, changing, or modifying attributes related to performance issues related to the system. its main role is to improve the performance of the system with the maximum accuracy result of the software output.

These changes raised during the maintenance phase are majorly related to initiated modifications to be done by the customer or users after the installation and testing phase, which includes bugs like defects uncovered during live uses of the system or requests raised by the customers. So the client is provided with timely and scheduled maintenance and support for the developed product. You will be amazed to know that the effort made in the design and development phase of the software product is only 60% compared to the efforts made in the maintenance phase.

There are three types of maintenance which are given below:

Corrective Maintenance: During the design and development phase, some errors are not discovered; they are only considered when the customer uses them. This is only corrective maintenance, which means correcting issues or errors not discovered in the development phase.
Perfective Maintenance: This maintenance is carried out on customer requests to increase and enhance the system’s or software’s functionalities.
Adaptive Maintenance: The maintenance required for switching the system environment and usually needed for porting the existing system to a new climate or computer or system or maybe with a new operating system. This phase is too important as this leads to better system performance.

So in the above discussion, we know each phase of the waterfall model deeply with full specifications. So we can say that the waterfall model is very important in the software field as compared to mechanical industries as each phase has its own importance, leading to a more productive and stable software.

Advantages and Disadvantages of Waterfall Model

Given below are the advantages and disadvantages mentioned:

Advantages:

It allows for departmentalization and control.
A schedule can be set with deadlines for each stage of development, and a product can proceed through the development process model phases one by one.
As it undergoes easily understandable and explainable phases, it overcomes many issues, making it very easy to use.
Due to the rigidity of the workflow model, it is very much easy to manage as each phase in the waterfall model has specific review and deliverables processes.
The waterfall model works well for smaller projects where requirements are very well understood.
The schedule can be set with deadlines for each stage of development, and a product can proceed through the development process model phases one by one.
Clearly defined stages.
Well-understood milestones.
Easy to arrange tasks.
Process and results are well documented.
Reinforces good habits: define-before-design.
Design-before-code.
The model works well for smaller projects and projects where requirements are well understood.

Disadvantages:

Not a good model for complex and object-oriented projects.
Not suitable for projects where requirements are at a moderate to high risk of changing.
Estimating the time and cost for each phase of the development process is difficult.
Not a good model for complex and object-oriented projects.
No working software is produced until late during the life cycle.
Cannot accommodate changing requirements.
It is difficult to measure progress within stages.
High amounts of risk and uncertainty.
Poor model for long and ongoing projects.
Adjusting scope during the life cycle can end a project.
No feedback path.
No overlapping of phases.
Difficult to accommodate change requests.
Risk and uncertainty are high with this process model.

Where to Use Waterfall Model?

Now, after encircling all the scenarios, we come to a point where we want to know where to use the waterfall model.

Majorly waterfall model is used in a defense project; the requirement is clear because before moving to the development phase, they analyze it well.
This can also be used in migration projects where requirements will be the same only platform or languages may vary / change.

Conclusion

So as a whole, we can say that the waterfall model is best suitable for small software development project as compared to big projects because design, development, and implementation is easier in the small project when working on waterfall model. After all, in this model, all the previous phases need to be completed when going to upcoming phases. So in the big project, the issues and errors come frequently as it has a large model. Every time, the testing phase will be continued if implemented through the waterfall model, which will lead to less optimization and accuracy of the software.

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