# Spiral model

## 1. Introduction 
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**Definition** :: Spiral model is a combination of systematic aspect of [[Waterfall Model|waterfall]] and iterative nature of [[Prototype Model|prototyping]] 
```ad-note
Spiral Model = systematic approach of **Waterfall** + iterative nature of **prototyping**
```

## 2. When to use spiral model? 
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- When software is big
- Need to solve as much risk as possible
- Requirments are complex
- Significant changes are aspected

## 3. Four fold procedure 
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1. Evoluation
2. Defining
3. Planning/Design
4. Engineering
  ![[Pasted image 20220206081420.png]]

## 4. Phases of Spira Model 
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- Requirement Analysis
- Prototyping
- Coding and testing
- Customer's Evoluation
![[Pasted image 20220205052425.png|Spiral model Diagram]]
## 5. Advatage 
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- The possibility of risk in the product signaficly reduce
- Very flexible
- Good for lard project
- Additional functionality can be added
- Software produces earlu

## 6. Disadvantage 
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- Waste for small project
- Highly depends on removing risk
- Need expertise for removing risk
- The success is depends on risk removing phase