Software Engineering - Old Questions

2. Describe spiral model with its advantages and disadvantages.

Spiral Model is a risk-driven software development process model. It is a combination of waterfall model and iterative model. Spiral Model helps to adopt software development elements of multiple process models for the software project based on unique risk patterns ensuring efficient development process.

In spiral model, total software development process activities are divided into four groups as shown in figure below:

1. Objectives determination and identify alternative solutions: Requirements are gathered from the customers and the objectives are identified, elaborated, and analyzed at the start of every phase. Then alternative solutions possible for the phase are proposed in this quadrant. 
   
2. Identify and resolve Risks: During the second quadrant, all the possible solutions are evaluated to select the best possible solution. Then the risks associated with that solution are identified and the risks are resolved using the best possible strategy. At the end of this quadrant, the Prototype is built for the best possible solution. 
   
3. Develop next version of the Product: During the third quadrant, the identified features are developed and verified through testing. At the end of the third quadrant, the next version of the software is available. 
   
4. Review and plan for the next Phase: In the fourth quadrant, the Customers evaluate the so far developed version of the software. In the end, planning for the next phase is started. 

Advantages:

• Changing requirements can be accommodated.
• Allows extensive use of prototypes.
• Requirements can be captured more accurately.
• Users see the system early.
• Development can be divided into smaller parts and the risky parts can be developed earlier which helps in better risk management.

Disadvantages:

• Management is more complex.
• End of the project may not be known early.
• Not suitable for small or low risk projects and could be expensive for small projects.
• Process is complex
• Spiral may go on indefinitely.