This paper compares three popular software development lifecycle (SDLC) models: waterfall, spiral, and prototype. The waterfall model follows a linear and structured approach, while the spiral model combines iterative phases with a focus on risk analysis, making it more flexible for complex projects. The prototype model emphasizes client feedback during development, allowing for adjustments but can also be costly and slow, highlighting that the choice of model depends on project-specific needs.

1. Running Head: THE WATERFALL, SPIRAL, AND PROTOTYPE SDLC MODELS 1
A Comparison of the Waterfall, Spiral, and Prototype SDLC Models
Teresa J. Rothaar
Wilmington University

2. THE WATERFALL, SPIRAL, AND PROTOTYPE SDLC MODELS 2
A Comparison of the Waterfall, Spiral, and Prototype SDLC Models
Introduction
There are numerous software/systems development lifecycle (SDLC) models. According
to Ruparelia (2010), each SDLC model can be classified in one of three categories: linear,
iterative, or a combination of both. Linear models are sequential; each stage automatically leads
into the next, and stages are not revisited or repeated. Iterative models are structured around the
idea that the SDLC is a continuous process, and each stage will be revisited multiple times
during the life of the project. A combined model is an iterative model with a finish line: It
acknowledges that, at some point, there will be no more need to revisit any of the stages (p. 8).
This paper will compare and contrast three popular SDLC models: waterfall, spiral, and
prototype.
The Waterfall Model
The term “waterfall” refers to a methodology as well as a model; software engineers
often use the term interchangeably (C. Seifer, personal communication, March 18, 2015). There
are actually two waterfall models: the traditional, linear model and a newer, iterative model.
Each model has five steps: requirements analysis, design, implementation, testing, and
maintenance (Maheshwari & Jain, 2012, p. 286).
In the traditional waterfall model, each step flows into the other sequentially. While some
“splash back” is permitted, the goal of the model is to move through each phase and onto the
next without repeating, with an “emphasis … on planning, time schedules, target dates, budgets
and implementation of an entire system at one time” (Maheshwari & Jain, 2012, p. 286). This
method is highly structured, with well-defined deliverables and milestones for each phase, which
make it easy to understand. However, the tight structure of the original waterfall model—in

3. THE WATERFALL, SPIRAL, AND PROTOTYPE SDLC MODELS 3
particular, the need to consider and plan for every possible eventuality at the beginning of the
project—has caused it to fall out of favor in today’s dynamic business environment. Often, the
project sponsor may not know exactly what they want at the outset, or, in the case of a large
project being done over a long period of time, something may change in the macro environment
that requires changes to the project (Maheshwari & Jain, 2012, p. 286).
Enter the iterative waterfall model. The steps are the same as in the traditional waterfall
method, but with testing and analysis at the end of each phase, which theoretically provides
valuable feedback when moving into the next phase. Additionally, unlike in the traditional
model, it is expected that phases will be repeated. The advantage of this model is that it is better
suited to the dynamic world of modern software and systems development; however, it lacks the
clear milestones of the original model and, thus, could be difficult to manage (Maheshwari &
Jain, 2012, p. 286-287).
The Spiral Model
Among the most flexible of SDLC models is the spiral model (Saxena & Kaushik, 2013,
p. 118), which is a combination of the traditional waterfall model and the prototype model
(Khurana & Gupta, 2012, p. 1516). It has four phases: requirements planning, risk analysis,
development and testing, and planning the next iteration. At the end of the risk analysis phase, a
prototype is produced, which is coded and tested in the third phase, then evaluated in the fourth
phase; feedback from this iteration is used to plan the next one. The hallmark of the spiral model
is its emphasis on risk analysis and mitigation, which makes it particularly suitable for very
large, costly projects (Khurana & Gupta, 2012, p. 1515-1516).
Figure 1 (Aafrin, 2012) visually demonstrates the similarities and differences between the
traditional waterfall and spiral models. The steps are very similar. However, while each step

4. THE WATERFALL, SPIRAL, AND PROTOTYPE SDLC MODELS 4
“falls” into the next when using waterfall, the spiral method keeps going around the “spiral” as
many times as necessary. While the method is considered iterative, it can be used as a
combination method, as eventually, the project will be finished and there will be no need to go
through further iterations:
Figure 1. A visual representation of the difference between the linear waterfall model and
the iterative spiral model.
The spiral model is not suitable for every project. Saxena and Kaushik (2013) note that,
among other drawbacks, it is very expensive and highly complex; there is no specified “finish
line,” and it can be difficult to determine when to stop going through the iterations; and it
requires that project managers have a high level of expertise in risk management. Thus, they
recommend that it be used only for large, highly complex, risky, and expensive projects (p. 118).
The Prototype Model
According to Maheshwari and Jain (2012), the prototype (or prototyping) model isn’t
solely a standalone model, though it can be used as one; it is an approach that can be
incorporated into any SDLC model (p. 287). For example, as discussed above, prototyping is an

5. THE WATERFALL, SPIRAL, AND PROTOTYPE SDLC MODELS 5
important part of the spiral model. Shukla and Saxena (2013) break the prototype model down
into six steps: requirements gathering; initial designing of the prototype; building the prototype;
having the client evaluate the prototype; refining the prototype; and finally, building the end
product (p. 19). As Figure 2 (ISTQB Exam Certification, 2012) illustrates, prototyping is a linear
method, like waterfall, with a beginning and an end:
Figure 2. A diagram of the prototype model.
Because it requires building a working model (which could end up being discarded), the
prototype model is expensive; however, it’s not as expensive as the spiral model (Shukla &
Saxena, 2013, p. 19). Other advantages include the fact that the client gets to see a working
model early in the project, which makes it easier for the client to make improvement suggestions,
may make it easier to get the project funded, and mitigates risk. However, costs can be high. The
development process can be slow, and as mentioned above, once feedback is received from the
client regarding the initial prototype, it may end up being useless. Additionally, the prototype
model encourages a lot of communication between the client and the developer; while this is
helpful in ensuring the client is happy with the final product, a non-technical client may expect
the moon and become upset when the developer cannot deliver on all requests as quickly and
inexpensively as the client thinks they should (Saxena & Kaushik, 2013, p. 119). Shukla and
Saxena (2013) recommend using this method only for small projects (p. 19).

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Conclusion
This paper discussed three popular SDLC models; many more exist. All of them include
phases for gathering requirements, performing a business analysis, designing the system,
implementing the system, and performing QA testing (Mishra & Dubey, 2013, p. 64). There is
no one “correct” model; all of them do the same thing, but use different problem-solving
approaches. The decision to choose one model over the other is dependent on the particular
situation under which an individual project is being developed.

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References
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