What is Spiral Model? When to Use? Advantages & Disadvantages

Details: Last Updated: 21 January 2019

What is Spiral Model?

Spiral Model is a combination of a waterfall model and iterative model. Each phase in spiral model begins with a design goal and ends with the client reviewing the progress. The spiral model was first mentioned by Barry Boehm in his 1986 paper.

The development team in Spiral-SDLC model starts with a small set of requirement and goes through each development phase for those set of requirements. The software engineering team adds functionality for the additional requirement in every-increasing spirals until the application is ready for the production phase.

Spiral Model Phases

Spiral Model Phases	Activities performed during phase
Planning	It includes estimating the cost, schedule and resources for the iteration. It also involves understanding the system requirements for continuous communication between the system analyst and the customer
Risk Analysis	Identification of potential risk is done while risk mitigation strategy is planned and finalized
Engineering	It includes testing, coding and deploying software at the customer site
Evaluation	Evaluation of software by the customer. Also, includes identifying and monitoring risks such as schedule slippage and cost overrun

When to use Spiral Methodology?

When project is large
When releases are required to be frequent
When creation of a prototype is applicable
When risk and costs evaluation is important
For medium to high-risk projects
When requirements are unclear and complex
When changes may require at any time
When long term project commitment is not feasible due to changes in economic priorities

Advantages and Disadvantages of Spiral Model

Advantages	Disadvantages
Additional functionality or changes can be done at a later stage	Risk of not meeting the schedule or budget
Cost estimation becomes easy as the prototype building is done in small fragments	It works best for large projects only also demands risk assessment expertise
Continuous or repeated development helps in risk management	For its smooth operation spiral model protocol needs to be followed strictly
Development is fast and features are added in a systematic way	Documentation is more as it has intermediate phases
There is always a space for customer feedback	It is not advisable for smaller project, it might cost them a lot