Waterfall Model – Software Engineering

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The Waterfall Model is a classical 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. It must be completed in a
specific order. This classical waterfall model is simple and idealistic. It was once
very popular. Today, it is not that popularly used. However, it is important because
most other types of software development life cycle models are a derivative of this.
In this article we will see 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.

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: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.
Phases of Waterfall Model
The Waterfall Model has six phases which are:
1. Requirements: The first phase involves gathering requirements from
stakeholders and analyzing them to understand the scope and objectives of the
project.
2. Design: Once the requirements are understood, the design phase begins. This
involves creating a detailed design document that outlines the software
architecture, user interface, and system components.
3. Development: The Development phase include implementation involves
coding the software based on the design specifications. This phase also includes
unit testing to ensure that each component of the software is working as
expected.
4. Testing: In the testing phase, the software is tested as a whole to ensure that it
meets the requirements and is free from defects.
5. Deployment: Once the software has been tested and approved, it is deployed to
the production environment.
6. Maintenance: The final phase of the Waterfall Model is maintenance, which
involves fixing any issues that arise after the software has been deployed and
ensuring that it continues to meet the requirements over time.

The classical waterfall model divides the life cycle into a set of phases. This model
considers that one phase can be started after the completion of the previous phase.
That is the output of one phase will be the input to the next phase. Thus the
development process can be considered as a sequential flow in the waterfall. Here
the phases do not overlap with each other. The different sequential phases of the
classical waterfall model are shown in the below figure.
 Waterfall Model-Software Engineering

Let us now learn about each of these phases in detail which include further phases.
1. Feasibility Study
The main goal of this phase is to determine whether it would be financially and
technically feasible to develop the software. The feasibility study involves
understanding the problem and then determining the various possible strategies to
solve the problem. These different identified solutions are analyzed based on their
benefits and drawbacks. The best solution is chosen and all the other phases are
carried out as per this solution strategy.
2. Requirements Analysis and Specification
The 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.
 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).
 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.
3. Design
The goal of this 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).
4. Coding and Unit Testing
In the coding 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.
5. Integration and System 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.
6. Maintenance
Maintenance 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.

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

 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.