The Spiral Model is an iterative software development process that is used for large, complex projects where requirements are not fully known. It consists of loops called phases that each have four quadrants - identification, design, construction, and evaluation. This allows for risk analysis, prototyping, customer evaluation and feedback at each phase of development. The Spiral Model supports risk handling, changing requirements, and customer involvement throughout the life cycle, making it well-suited for complex projects, though it is more complex and expensive than other models.

1. Spiral Model
Software Development Life Cycle (SDLC)

2. Spiral Model
★ It is best suited for complex embedded product development & situations
where the requirements are changing from customers side.
★ It supports Risk Handling by evaluating the risks in each stage.
★ It is a combination of Waterfall model & Iterative model.
★ The exact number of loops of the spiral is unknown and can vary from
project to project.
★ Each loop of the spiral is called a Phase of the software development process.

3. Spiral Model
★ Each phase of Spiral Model is divided into four quadrants.
Identification
Designing
Construction
Evaluation

4. Spiral Model
IDENTIFICATION
➔ This phase starts with gathering the requirements.
➔ This phase also includes understanding the system
requirements by continuous communication between the
customer and the system analyst.
➔ The objectives are identified, elaborated and analyzed at the
start of every phase.

5. Spiral Model
DESIGNING
➔ This involves architectural design, logical design of modules,
physical product design and the final design in the subsequent
spirals.
➔ At the end of this quadrant, Prototype is built.

6. Spiral Model
CONSTRUCTION
➔ This phase refers to production of the actual software
product.
➔ The identified features are developed and verified through
testing.
➔ At the end of the third quadrant, a new version of the
software is available.
➔ These builds are sent to the customer for feedback.

7. Spiral Model
EVALUATION
➔ In the fourth quadrant, the Customers evaluate the so far
developed version of the software.
➔ The software development process enters the next iteration
and subsequently follows the linear approach to implement the
feedback suggested by the customer.
➔ The process of iterations along the spiral continues
throughout the life of the software.

8. Advantages & Disadvantages
❏ Supports Risk Handling
❏ Best suited for large projects
❏ Flexibility in Requirements
❏ Customer Satisfaction
❏ More complex than other SDLC models
❏ Not suitable for small projects as it is expensive
❏ Too much dependable on Risk Analysis
❏ Difficulty in time management