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The waterfall model is a sequential software development process, in which progress is seen as flowing steadily downwards (like a waterfall) through the phases of Conception, Initiation, Analysis, Design, Construction, Testing and Maintenance.
The waterfall development model has its origins in the manufacturing and construction industries; highly structured physical environments in which after-the-fact changes are prohibitively costly, if not impossible. Since no formal software development methodologies existed at the time, this hardware-oriented model was simply adapted for software development.
Advantages of Waterfall Life Cycle Models
1. Easy to explain to the user2. Stages and activities are well defined3. Helps to plan and schedule the project4. Verification at each stage ensures early detection of errors / misunderstanding
SPIRAL MODEL
The spiral model is a software development processes combining which elements of both design and prototyping-in-stages, in an effort to combine advantages of top-down and bottom-up concepts. Also known as the spiral lifecycle model (or spiral development), it is a systems development method (SDM) used in information technology (IT). This model of development combines the features of the prototyping model and the waterfall model. The spiral model is intended for large, expensive and complicated projects.