Waterfall Model - Software Engineering

The Waterfall Model is a Traditional Software Development Methodology. It was first introduced by Winston W. Royce in 1970. It is a linear and sequential approach to software development that consists of several phases.

This classical waterfall model is simple and idealistic. It is important because most other Types of Software Development Life Cycle Models are a derivative of this. In this article, we will see the Waterfall Model in detail.

What is the SDLC Waterfall Model?

The waterfall model is a Software Development Model used in the context of large, complex projects, typically in the field of information technology. It is characterized by a structured, sequential approach to Project Management and Software Development.

The Waterfall Model is useful in situations where the project requirements are well-defined and the project goals are clear. It is often used for large-scale projects with long timelines, where there is little room for error and the project stakeholders need to have a high level of confidence in the outcome.

Read more:  Software Development Life Cycle (SDLC) Models

Phases of Waterfall Model

Classical Waterfall Model divides the life cycle into a set of phases. The development process can be considered as a sequential flow in the waterfall. The different sequential phases of the classical waterfall model are follow:

Let us now learn about each of these phases in detail which include further phases.

1. Requirements Analysis and Specification

Requirement Analysis and specification phase aims to understand the exact requirements of the customer and document them properly. This phase consists of two different activities. 

1. Requirement Gathering and Analysis: Firstly all the requirements regarding the software are gathered from the customer and then the gathered requirements are analyzed.

The goal of the analysis part is to remove incompleteness (an incomplete requirement is one in which some parts of the actual requirements have been omitted) and inconsistencies (an inconsistent requirement is one in which some part of the requirement contradicts some other part).

2. Requirement Specification: These analyzed requirements are documented in a software requirement specification (SRS) document. SRS document serves as a contract between the development team and customers. Any future dispute between the customers and the developers can be settled by examining the SRS document.

2. Design

The goal of this Software Design Phase is to convert the requirements acquired in the SRS into a format that can be coded in a programming language. It includes high-level and detailed design as well as the overall software architecture. A Software Design Document is used to document all of this effort (SDD).

• High-Level Design (HLD): This phase focuses on outlining the broad structure of the system. It highlights the key components and how they interact with each other, giving a clear overview of the system’s architecture.
• Low-Level Design (LLD): Once the high-level design is in place, this phase zooms into the details. It breaks down each component into smaller parts and provides specifics about how each part will function, guiding the actual coding process.

3. Development

In the Development Phase software design is translated into source code using any suitable programming language. Thus each designed module is coded. The unit testing phase aims to check whether each module is working properly or not. 

• In this phase, developers begin writing the actual source code based on the designs created earlier.
• The goal is to transform the design into working code using the most suitable programming languages.
• Unit tests are often performed during this phase to make sure that each component functions correctly on its own.

4. Testing and Deployment

1. Testing: Integration of different modules is undertaken soon after they have been coded and unit tested. Integration of various modules is carried out incrementally over several steps. During each integration step, previously planned modules are added to the partially integrated system and the resultant system is tested. Finally, after all the modules have been successfully integrated and tested, the full working system is obtained and system testing is carried out on this. System testing consists of three different kinds of testing activities as described below.

• Alpha testing: Alpha testing is the system testing performed by the development team.
• Beta testing: Beta testing is the system testing performed by a friendly set of customers.
• Acceptance testing: After the software has been delivered, the customer performs acceptance testing to determine whether to accept the delivered software or reject it.

2. Deployment: Once the software has been thoroughly tested, it's time to deploy it to the customer or end-users. This means making the software ready and available for use, often by moving it to a live or staging environment.

During this phase, we also focus on helping users get comfortable with the software by providing training, setting up necessary environments, and ensuring everything is running smoothly. The goal is to make sure the system works as expected in real-world conditions and that users can start using it without any hitches.

5. Maintenance

In Maintenance Phase is the most important phase of a software life cycle. The effort spent on maintenance is 60% of the total effort spent to develop a full software. There are three types of maintenance.

• Corrective Maintenance: This type of maintenance is carried out to correct errors that were not discovered during the product development phase.
• Perfective Maintenance: This type of maintenance is carried out to enhance the functionalities of the system based on the customer’s request.
• Adaptive Maintenance: Adaptive maintenance is usually required for porting the software to work in a new environment such as working on a new computer platform or with a new operating system.

Features of Waterfall Model

Following are the features of the waterfall model:

1. Sequential Approach: The waterfall model involves a sequential approach to software development, where each phase of the project is completed before moving on to the next one.
2. Document-Driven: The waterfall model depended on documentation to ensure that the project is well-defined and the project team is working towards a clear set of goals.
3. Quality Control: The waterfall model places a high emphasis on quality control and testing at each phase of the project, to ensure that the final product meets the requirements and expectations of the stakeholders.
4. Rigorous Planning: The waterfall model involves a careful planning process, where the project scope, timelines, and deliverables are carefully defined and monitored throughout the project lifecycle.

Overall, the waterfall model is used in situations where there is a need for a highly structured and systematic approach to software development. It can be effective in ensuring that large, complex projects are completed on time and within budget, with a high level of quality and customer satisfaction.

Importance of Waterfall Model

Following are the importance of waterfall model:

1. Clarity and Simplicity: The linear form of the Waterfall Model offers a simple and unambiguous foundation for project development.
2. Clearly Defined Phases: The Waterfall Model phases each have unique inputs and outputs, guaranteeing a planned development with obvious checkpoints.
3. Documentation: A focus on thorough documentation helps with software comprehension, maintenance, and future growth.
4. Stability in Requirements: Suitable for projects when the requirements are clear and stable, reducing modifications as the project progresses.
5. Resource Optimization: It encourages effective task-focused work without continuously changing contexts by allocating resources according to project phases.
6. Relevance for Small Projects: Economical for modest projects with simple specifications and minimal complexity.

Example of Waterfall Model

Here we can take a Real world example of the Waterfall Model.

Real-Life Example of Waterfall Model: Developing an Online Banking System

1. Analysis

This phase will be tasked with gathering all the information available on customer banking requirements, transactions, security protocols, and devising the different parameters that’ll be used for determining the core functionalities of the online banking system, such as account management, fund transfers, bill payments, and loan applications.

2. Design

In this example of the Waterfall Model, the design phase is all about fine-tuning the parameters established in the analysis phase. The system’s architecture will be designed to manage sensitive data securely, avoid transactional errors, and ensure high performance. This includes database structure, user interface design, encryption protocols, and multi-factor authentication to protect user accounts.

3. Implementation

This all-important phase involves doing dummy runs of the online banking system with a provisional set of banking transactions and customer data to see the accuracy with which the system can handle transactions, balance inquiries, fund transfers, and bill payments. These results should be matched with results from banking experts and auditors who ensure compliance with banking regulations and accuracy in transactions.

4. Testing

As with any example of the Waterfall Model, the testing phase is about ensuring that all features of the online banking system function smoothly. This includes testing for security vulnerabilities, transaction accuracy, performance under heavy load, and user interface responsiveness. Special attention is given to testing secure logins, data encryption, and ensuring that sensitive data is handled correctly throughout the system.

5. Maintenance

In the final phase, the online banking system should be checked for any necessary updates or alterations that may be required, besides the expected inclusion of new features or changes in banking regulations. Regular updates will also be needed for security patches, performance improvements, and the addition of new services like mobile banking, instant loans, or personalized financial advice.

Advantages of Waterfall Model

The classical waterfall model is an idealistic model for software development. It is very simple, so it can be considered the basis for other software development life cycle models. Below are some of the major advantages of this SDLC model.

• Easy to Understand: The Classical Waterfall Model is very simple and easy to understand.
• Individual Processing: Phases in the Classical Waterfall model are processed one at a time.
• Properly Defined: In the classical waterfall model, each stage in the model is clearly defined.
• Clear Milestones: The classical Waterfall model has very clear and well-understood milestones.
• Properly Documented: Processes, actions, and results are very well documented.
• Reinforces Good Habits: The Classical Waterfall Model reinforces good habits like define-before-design and design-before-code.
• Working: Classical Waterfall Model works well for smaller projects and projects where requirements are well understood.

Disadvantages of Waterfall Model

The Classical Waterfall Model suffers from various shortcomings we can’t use it in real projects, but we use other software development lifecycle models which are based on the classical waterfall model. Below are some major drawbacks of this model.

• No Feedback Path: In the classical waterfall model evolution of software from one phase to another phase is like a waterfall. It assumes that no error is ever committed by developers during any phase. Therefore, it does not incorporate any mechanism for error correction. 
• Difficult to accommodate Change Requests: This model assumes that all the customer requirements can be completely and correctly defined at the beginning of the project, but the customer's requirements keep on changing with time. It is difficult to accommodate any change requests after the requirements specification phase is complete. 
• No Overlapping of Phases: This model recommends that a new phase can start only after the completion of the previous phase. But in real projects, this can't be maintained. To increase efficiency and reduce cost, phases may overlap. 
• Limited Flexibility: The Waterfall Model is a rigid and linear approach to software development, which means that it is not well-suited for projects with changing or uncertain requirements. Once a phase has been completed, it is difficult to make changes or go back to a previous phase.
• Limited Stakeholder Involvement: The Waterfall Model is a structured and sequential approach, which means that stakeholders are typically involved in the early phases of the project (requirements gathering and analysis) but may not be involved in the later phases (implementation, testing, and deployment).
• Late Defect Detection: In the Waterfall Model, testing is typically done toward the end of the development process. This means that defects may not be discovered until late in the development process, which can be expensive and time-consuming to fix.
• Lengthy Development Cycle: The Waterfall Model can result in a lengthy development cycle, as each phase must be completed before moving on to the next. This can result in delays and increased costs if requirements change or new issues arise.

When to Use Waterfall Model?

Here are some cases where the use of the Waterfall Model is best suited:

• Well-understood Requirements: Before beginning development, there are precise, reliable, and thoroughly documented requirements available.
• Very Little Changes Expected: During development, very little adjustments or expansions to the project's scope are anticipated.
• Small to Medium-Sized Projects: Ideal for more manageable projects with a clear development path and little complexity.
• Predictable: Projects that are predictable, low-risk, and able to be addressed early in the development life cycle are those that have known, controllable risks.
• Regulatory Compliance is Critical: Circumstances in which paperwork is of utmost importance and stringent regulatory compliance is required.
• Client Prefers a Linear and Sequential Approach: This situation describes the client's preference for a linear and sequential approach to project development.
• Limited Resources: Projects with limited resources can benefit from a set-up strategy, which enables targeted resource allocation.

The Waterfall approach involves less user interaction in the product development process. The product can only be shown to end user when it is ready.

Applications of Waterfall Model

Here are some application of SDLC waterfall model:

• Large-scale Software Development Projects: The Waterfall Model is often used for large-scale software development projects, where a structured and sequential approach is necessary to ensure that the project is completed on time and within budget.
• Safety-Critical Systems: The Waterfall Model is often used in the development of safety-critical systems, such as aerospace or medical systems, where the consequences of errors or defects can be severe.
• Government and Defense Projects: The Waterfall Model is also commonly used in government and defense projects, where a rigorous and structured approach is necessary to ensure that the project meets all requirements and is delivered on time.
• Projects with well-defined Requirements: The Waterfall Model is best suited for projects with well-defined requirements, as the sequential nature of the model requires a clear understanding of the project objectives and scope.
• Projects with Stable Requirements: The Waterfall Model is also well-suited for projects with stable requirements, as the linear nature of the model does not allow for changes to be made once a phase has been completed.

For more, you can refer to the Uses of Waterfall Model.

Conclusion

The Waterfall Model has good conventional Software Development Processes. This model is sequential technique provides an easily understood and applied structured framework. Here we learned the Waterfall model in detail.