We’re back for another installation in our series about SDLC models. This installation is the Spiral model.
The Spiral model is among the more important Software Development Life Cycle models as it deals with Risk Handling.
When you look at a visual representation of the Spiral model, you see how it got its name—it is laid out like a spiral with many loops. How many loops a Spiral model has is unknown and depends upon each individual project.
The individual loops are referred to as a “phase” in the software development process. Furthermore, the number of phases needed to complete a given project varies by project manager and project risk.
The radius of the spirals is representative of the current cost of the project at that given point.
Additionally, the angular dimension of the spirals show how far you’ve progressed in your current phase.
The 4 Cycles of the Spiral Model
Like many of the other SDLC models, the first phase involves gathering the requirements. This serves as the baseline for the spiral.
In the next spirals (as your project grows) are system requirements, subsystem requirements and unit requirements.
Additionally, this stage involves learning the system requirements while allowing constant communication between analysts and customers.
To begin the design phase, all of the elements involved with the baseline are combined and the project moves into the architectural design, logical design, product design and final design in the next spirals.
In the construct phase, the actual production of the software occurs in each representative spiral.
During the baseline spiral, the product is just conceptual; however, there is a Proof of Concept to get customer feedback.
As the model adds spirals, there is increased information on the project requirements and the actual details of the design are laid out. These are referred to as “builds” and each has a unique version number.
Additionally, the builds receive feedback from the customers.
4. Evaluation and Risk Analysis
During this phase, the risk analysis takes place. Risk analysis involves estimating, identifying and monitoring all of the feasible parts and risks of the project.
After testing (which occurs at the end of the first iteration) your customer will assess the product and will send you feedback on any changes needed.
The Pros (and Cons) of the Spiral Method
One advantage of utilizing a spiral SDLC model is that it allows users to add elements into the project as they become needed. Using this method means that you won’t run into conflicts with previous designs.
Another benefit is that the spiral model allows for consistency even among multiple builds and releases. The spiral lifecycle model allows elements of the product to be added in once they become known or available. This assures that there is no conflict with previous requirements and design.
Conversely, the Spiral model involves very strict management.
Additionally, there is some risk of initializing an indefinite loop.
Another big disadvantage is that this model isn’t typically suitable for small or medium businesses.