Learn in the textbookClassic Software Development Models
DefinitionThe spiral model (スパイラルモデル) splits a system into parts and, by repeating a development cycle from planning to evaluation for each part, spirals toward completion.
ExplanationEach loop starts with a plan and an estimate of likely trouble spots (risks, リスク) before moving to design and prototyping, and the evaluation results feed into the next loop's plan. With every loop the scope of development widens, and the system gradually nears completion.
AnalogyIt is like planting flowers in one corner of a garden, seeing how they grow, and then using what you learned to extend the flower bed to the next patch, again and again.
Memory hookPicture a spiral: each time the work loops back from evaluation to the next plan, it reaches a little further out.