Spiral development process assumes that customer requirements are obtained in multiple iterations, and development also works in iterations. Many big software systems are built by spiral models of ever-increasing size. First some functionalities are added, then product is created and released to customer. After getting the benefits of first iteration of implementation, the customer may add another chunk of requirements to the existing one. Further addition of requirements increase the size of the software spirally. Sometimes, an individual part developed in stages represents a complete system, and it may communicate with the next developed system through some interfaces.
In many ERPs, initial development concentrated around material management part which later increased spirally to other parts such as purchasing, manufacturing, sales, warehousing, cash control, etc. Many banking software’s also followed a similar route. Figure 2.5 shows a spiral development model.
Spiral development is considered as miniature form of the incremental model.