1) Waterfall Model :-
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DISADVANTAGES
- Real time projects rarely flow sequentially.
- It is often difficult for the customer to state all the requirements at a time.
- Customer need to be tolerant as the working model cannot be viewed unless last phase ends.
- Any mistake left untouched will not get discovered and corrected till last phase.
There are also a few things like low budget and no periodic feedback from the stakeholders to correct any feature with which they may not be satisfied with. In short, waterfall model is very rigid, and can be applied only on very small level, if at all.
2) Spiral Model :-
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-Risk driven process model
- Anchor point milestones: a combination of work products and conditions that are attained along the path of the spiral—are noted for each evolutionary pass.
- Applicable for large scale projects
- Is an evolutionary software process model that couples the iterative nature of prototyping with the controlled and systematic aspects of the waterfall model.
- It provides the potential for rapid development of increasingly more complete versions of the software.
- The first circuit around the spiral might result in the development of a product specification; subsequent passes around the spiral might be used to develop a prototype and then progressively more sophisticated versions of the software.
- Each pass through the planning region results in adjustments to the project plan.
- Cost and schedule are adjusted based on feedback derived from the customer after delivery.
- In addition, the project manager adjusts the planned number of iterations required to complete the software.
- Unlike other process models that end when software is delivered, the spiral model can be adapted to apply throughout the life of the computer software
DISADVANTAGES :
▪ It may be difficult to convince customers (particularly in contract situations) that the evolutionary approach is controllable.
▪ It demands considerable risk assessment expertise and relies on this expertise for success. If a major risk is not uncovered and managed, problems will undoubtedly occur.