Difference Between Waterfall Model and Spiral Model (with Comparison Chart)

Waterfall Vs Spiral Model The Waterfall and Spiral models are the process models used for developing software in a well-defined, systematic and cost-effective way. The major difference between these software process models waterfall and the spiral is that the waterfall model is comprised of the separate and isolate phases of specification and development. On the other hand, in a spiral model the different specification, development and validation phases are interleaved.

These process model are a crucial part of software engineering while creating two software products by implementing two different processes the theoretical planning would be similar but its results would not appear similar. So, by following a process model we can control various activities required to develop and maintain the software. The benefits of software process model involve – helps in achieving effective communication, process reuse and provides process management. It just takes some requirements as input and produces and deliver products as output.

Content: Waterfall Model Vs Spiral Model

Comparison Chart

Basis for comparison	Waterfall Model	Spiral Model
Basic	Model follows a sequential approach.	Model is based on an evolutionary approach.
Process involves	Stages or phases	Task regions
Requirement	Needs a thorough understanding of requirements from the beginning.	Requirements can be added up in the new iterations if required.
Risk management	Risks can only be detected during the completion of the model.	Risks are identified and rectified earlier.
Working model of the product	Can only be generated in the end.	Each iteration produces a working model.
Preferred by	Customers	Developers
Suitable for	Small systems	Large systems

Definition of Waterfall Model

The waterfall model is a classical software life cycle model. The model’s flow is sequential as the suggests similar to a waterfall in a top-down fashion, that is the reason it is also known as the linear sequential model. It has various phases such as requirement analysis, design, coding, testing, integration, implementation and maintenance, which we discuss below in detail.

However, in this model if a phase has completed we can not alter it, means that whatever is done in the previous phase could be changed. The process flow could not pass through the bottom to top it always flow from top to bottom and this makes it crucial to be completely preplanned to reduce the chances of product failure.

Phases of the Waterfall Model

Feasibility Study – In this stage, the cost and benefits are evaluated of the proposed application. The feasibility analysis should produce a document containing – definition of the problem, discovering the technical and economic viability, alternate solutions, needed resources, cost and delivery dates.
Requirement Analysis and specifications – This helps in finding gathering the requirements of the project what the project is needed. It determines the quality of the project such as functionality, ease of use, performance, portability, etc. The Software Requirement Specification (SRS) document contains – thorough statement of the problem, probable substitute solution to the problem, functional requirement of the software system, constraints on the software system.
Design – This phase is a multistep process concentrates on four different attributes of a program: data structure, software architecture, interface representations and algorithmic details. The design phase converts the requirement specification into the representation of the software that can be evaluated before the coding phase.
Coding and Module Testing – The design must be converted into a machine-readable form in order to produce software so in this step we actually write programs with the help of programming languages. While the module testing involves the definition of a test plan, the definition of the testing criteria to be followed (such as black-box or white-box or combination of the two), the definition of completion criteria (when to cease it) and at last management of test cases.
Integration and System Testing – This phase combines the modules of the software in a systematic and planned manner. The integration of the modules can no be conducted in one go but require several iterations. Furthermore, system testing is carried out to check whether the software system works as described in the SRS document. The three phases of system testing are- alpha, beta and acceptance testing.
Delivery and Maintenance – After delivering the product it is analysed for some period to detect and correct the errors which don’t show up in early stages of software, and this is known as maintenance.

Definition of Spiral Model

The spiral model is an evolutionary type of software life cycle model which merges the features of the prototype model and waterfall model. It has the potential for developing the incremental versions of the softwares by implementing the iterativeness of the prototype model and controlled methodical of the linear segmental model. The outcome of the spiral model is the series of the incremental releases of the software.

It is a realistic approach to develop large-scale systems and software. In the core or initial pass of the process, the product specification is formed. In succeeding passes round the spiral, the prototype gets developed. Further then more improved variants of the software get developed. These prototypes are evaluated and validated by customers. It also analyses risk at each pass. The project starts by defining the entry axis points in the spiral model.

It works by dividing the model into framework activities, which are known as task regions. Basically, there are three to six task regions could present such as customer communication, planning, risk analysis, engineering and so on which are described below.

Task regions of Spiral Model

Customer communication – It must enable effective communication between the various tasks.
Planning – This region involves all project related activities such as defining resources, timelines, etcetera.
Risk analysis – The technical and management risks are evaluated in this task.
Engineering – This task region is modelled for constructing one or more representations of applications executing.
Construct and release – It carries out all the important tasks needed to build, test, install the application and also provides user support.
Customer evaluation – This task region obtain customer’s feedback on the basis of customer evaluation and implement it at the installation stage.

Key Differences Between Waterfall Model and Spiral Model

The waterfall model is analogous to a waterfall which follows a sequential approach for its stages while developing a product. On the contrary, the spiral model is founded on an evolutionary strategy where a spiral is subdivided into several task regions.
Requirement gathering in both of the models is completely different where waterfall do it once in the whole process. As against, in a spiral model, the requirement can be gathered after each iteration.
Risks to the product can only be identified at the end of the process in the waterfall model. Conversely, the spiral model recognizes risk at earlier phases of the process which is revised at each iteration too.
The waterfall model produces the single final product at the end of the process. In contrast, the spiral model generates a rough working product at each iteration.
Waterfall model is suitable for small systems while spiral is preferred when the large system is developed.

Conclusion

The spiral model is different from waterfall model due to the feature of definite identification of the risk which reduces the chances of failure of the project. On the other hand, the waterfall is quite risky as there are no iterations everything have to be done at once meaning the requirements are gathered, planned, designed, coded, integrated at one time for a software product.