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Everything about the classical Waterfall Model

  • Bhumika Dutta
  • Aug 27, 2022
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Today, we have software for everything, which greatly simplifies our life. A large team of designers and developers is working behind the scenes to make this software usable; they do not just suddenly arise. Analyzing user requirements, designing, developing, and testing the resulting software are all steps in the process known as software engineering.


Every software requires a development time, known as the Software Development Life Cycle (SDLC). There are many process models for the developers to follow while making the software. These process models were introduced to divide the work of development into smaller and sequential portions, improve the quality of the software, and reduce the development time.


In this article, we are going to learn about the first SDLC Model to be introduced, known as the Waterfall Model. 



What is the Waterfall Model?


The waterfall model is the first process model introduced in the field of software design. 


It was introduced by Winston Royce in 1970. It was named so because the diagrammatic representation of this model represents a cascading waterfall. The main aim of this model was to divide the work among the team members to eradicate confusion and chaos. 


It is a type of Linear Sequential life cycle Model. This implies that a phase of development can only start if the one before it is finished. The stages in this waterfall model don't cross over.


Speaking of phases, the waterfall model has five main phases:


  • Requirement analysis and specifications

  • Design

  • Implementation and unit testing

  • Integration and system testing

  • Operation and Maintenance

The waterfall model (source) 

These steps are followed after checking the feasibility of the project. Finding out if developing the program would be technically and financially possible is the major purpose of a feasibility study.


Understanding the issue and identifying potential solutions are the first steps in the feasibility study. The advantages and disadvantages of the various solutions are considered, and the best option is selected. 


If the said project is feasible and meets all the requirements, then the next phases are then carried out following this solution approach.


Let us understand these steps one by one now.


1. Requirement Analysis and Specification:


This phase is mainly to understand the exact requirements of the customer. In this phase, the customer works closely with the developer to discuss the properties of the software and if it is possible for the developer to build it. 


They gather all the functions, performances, and interfacing requirements of the software, which are then documented by the developing company. This phase removes the ‘incompleteness’ and ‘inconsistency’  of the project.


During this stage, a sizable document known as the Software Requirement Specification (SRS) paper is produced, containing a thorough explanation in the plain language of what the system will do.


Deliverables of this phase include:


  • RUD (Requirement Understanding Document), OR

  • SDD (Software Requirement Specification) document


2. System Design:


The requirements presented in the SRS are coded in this phase. The developer studies all the needs of the software and works with the designing team to build the software into a usable and functional program. 


It provides high-level and extensive signs in addition to defining the overall program architecture. A Software Design Document (SDD) serves as a record of all of this effort.


Deliverables of this phase include:


  • HLD (High-Level Design Document)

  • LLD (Low-level Design Document)


3. Implementation and Unit Testing:


Once the developer completes the coding of the software along with the interfaces, the design is then implemented in this phase. All the information is collected from the SDD and followed accordingly.


The code is carefully reviewed and changed throughout testing. Small modules are initially tested separately. This is known as unit testing. The goal of the unit testing step is to determine whether or not each module is functioning correctly. The interaction between these modules and the flow of intermediate output is then checked by generating some overhead code.


Deliverables of this phase include:


  • Unit test cases and results

  • Programs of the software


Also Read | What is Integration Testing?


4. Integration and System Testing:


This is one of the most crucial steps of this model as it determines the quality of the software. Customer satisfaction, fewer maintenance costs, and precise findings will all benefit from the improved production.


In the previous step, unit testing was carried out that checked the functionality of the modules individually. But, in this step, the modules are integrated and tested as a system. This is done to check the interactions of the modules with one another, and with the system.


Finally, a completely functional system is obtained and tested when all the modules have been successfully integrated and tested.


Many types of testing can be done, but these are the three main types:


  • Alpha Testing:


Before distributing the product to actual consumers, the development team often does this testing to find issues (clients or the public). One of the user acceptability tests is this one.


  • Beta Testing:


Beta testing is carried out in a genuine setting by actual users of the software program. Another sort of user acceptance testing is beta testing.


  • Acceptance testing:


The customer carried out acceptance testing to decide whether to accept or reject the provided software once it had been delivered.


They also test the application for regression to check if any new flaws have emerged.


Deliverables of this phase include:


  • User Manual

  • Specifications of the environment


Also Read | Types of Testing


5. Operation and Maintenance Phase:


Once the program has been provided to the client, installed, and operating, maintenance is the work carried out by each user. The time required to maintain a software system accounts for 60% of the time required to construct a complete software system. 


There are three different kinds of maintenance:


  • Corrective Maintenance:


This kind of upkeep is done to fix faults that weren't found during the product creation stage.


  • Perfective Maintenance:


Based on the customer's request, this form of maintenance is done to improve the system's functions.


  • Adaptive Maintenance:


When transferring software to a new environment, such as working on a new computer platform or with a new operating system, adaptive maintenance is typically necessary.


Deliverables of this phase include:


  • User Manual

  • List of production tickets

  • List of new features implemented.


When should we use a Waterfall Model?


The waterfall model is a little obsolete today, but it can be still used in scenarios where:


  1. Because there is no possibility of modifying criteria in the future, requirements are seldom changed and customers are crystal clear about what they want as the result of the program they wanted to be built.


  1. The software to be built is not very complicated. For instance, compact standalone programs like supply chain management systems, human resource management systems (HRMS), and customer relationship management systems (CRM systems).


  1. The application's technology and tools do not change over time.


What are the advantages of the Waterfall Model?


The ability to departmentalize and exercise control is one of waterfall development's benefits. A product can move through the stages of the development process model one at a time by setting deadlines for each step and following a timetable.


Conceptualization is followed by design, implementation, testing, installation, troubleshooting, and finally operation and maintenance in the development process. The stages of development are carried out in a certain order.


Here are the advantages of this model:


  1. This model is simple and easy to understand. It does not over-complicate the steps.

  2. Because of the rigor of the model and the fact that each phase has a set of deliverables and a review procedure, it is simple to manage.

  3. This model processes and completes steps one at a time. Phases don't cross across.

  4. For smaller projects with well-defined and well-understood needs, the waterfall approach is effective.


What are the disadvantages of the Waterfall Model?


The traditional waterfall model has several flaws that prevent us from using it in actual projects. Instead, we utilize different software development lifecycle models that are based on the traditional waterfall model.


Here are some disadvantages of this model:


  1. If the requirements change or are adjusted in the middle of the model's implementation, there is a significant risk and degree of uncertainty.

  2. Software evolves like a cascade from one phase to the next in the traditional waterfall paradigm. It is predicated on the idea that developers never make mistakes at any stage. This means that it lacks any method for mistake correction.

  3. It should not be used for projects where there is a moderate to a high probability of requirement changes because otherwise, the outcomes could grow worse.

  4. This approach advises waiting till the preceding phase is finished before beginning a new one. This, however, cannot be maintained in actual projects. Phases may overlap for cost- and efficiency-saving reasons.

  5. Since no prototype may be shown during the intermediate phases, the ultimate result is delivered when the waterfall model's flow is complete.

  6. The client's helpful suggestions cannot be included in the period of continued development.

  7. Testing is done later than other phases of the process, making it harder to identify barriers and hazards early on. This increases the risk since there is a probability that there may be inconsistencies in the intermediate stages that will impact the outcome of later phases.


Also Read | An Overview of Agile Development Cycle


Some examples of the Waterfall Model:


Enterprise applications including Customer Relationship Management (CRM) systems, Human Resource Management (HRMS), Supply Chain Management Systems, Inventory Management Systems, Point of Sale (POS) systems for Retail chains, etc. were once developed using the Waterfall paradigm.


Up to the year 2000, the waterfall approach was extensively utilized in the creation of software. Even after the 2001 publication of the Agile Manifesto, many organizations employed the Waterfall methodology in the past years.


Nowadays, depending on the needs of the project, the majority of projects use Agile Methodology, an iterative model, or another methodology. Applications created using the Waterfall Model in the past, such as CRM systems and supply chain management systems, would often take a year or longer to construct.


Today, the waterfall model is preferred by the Development of Department Of Defense (DOD), military and aircraft programs. 


How are Agile Models different from the Waterfall Model?


As you have read, the waterfall model is a sequential model, and it takes a lot of planning beforehand as you cannot go back to any step. This is one advantage of the agile models over waterfall models as it is practically not always possible for the clients to know what they want. Agile models do not require long term planning as the required product is delivered within 2-4 weeks. 


Waterfall models follow a hierarchy, usually all the communications take place during the planning phase and the testing phase, and everything is governed by someone from the top. This is not the case in agile projects. Usually the team members communicate thoroughly throughout the entire project and self-govern. There is no one on the top that can look after the entire thing.


Another advantage of the agile model over the waterfall model is that it is very open to change, and significantly more user dependent. This is important because it leads to better user experience, which should be the ultimate goal of any software  development. 


It is very difficult to measure the progress of the project or quality control in between the development process in waterfall models as well, which can often lead to disappointment and project failure at the end. This is also fixed by the agile methodologies, where quality control activities are performed throughout the project. 


Also Read | AGILE Business Analyst - An Overview




The waterfall approach stresses the significance of signing off on each phase's deliverables. With all of these advantages, the Agile and Prototype methods currently dominate most projects, with the Waterfall approach still being effective for smaller projects. 


The Waterfall methodology will produce the greatest outcomes if the requirements are simple and testable. Waterfall models are cheaper and more strategic, although very impractical in today's world. In this article, we have discussed all about the classical Waterfall Model that once brought a revolution in the software development lifecycle process.

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