Iterative Model and Incremental Model - DavidMyrseth/BuketovPY GitHub Wiki

Iteration and Incrementation Models in Software Development

Iteration and incrementation are two fundamental approaches used in software development models to manage complexity, improve flexibility, and deliver functional software progressively. These concepts are often combined in modern Agile and iterative methodologies.

1. Iterative Model

Definition:

The iterative model involves developing a software system through repeated cycles (iterations), where each iteration refines and expands the product based on feedback.

Key Characteristics:

  • The software is built in repeated cycles (iterations).
  • Each iteration produces a working version of the product, which improves over time.
  • Feedback from stakeholders is incorporated in subsequent iterations.
  • Works well when requirements are not fully defined at the beginning.

Phases in Each Iteration:

  1. Planning – Define objectives for the iteration.
  2. Design & Development – Build features for the current iteration.
  3. Testing & Evaluation – Validate functionality and gather feedback.
  4. Review & Refinement – Adjust requirements and plan the next iteration.

Advantages:

✔ Early delivery of partial solutions.
✔ Easier to incorporate changes.
✔ Reduces risks by detecting issues early.

Disadvantages:

✖ Requires strong project management.
✖ Can lead to scope creep if not controlled.

Examples of Iterative Models:

  • Spiral Model (Combines iteration with risk analysis)
  • Agile Models (Scrum, Kanban – iterative and incremental)

2. Incremental Model

Definition:

The incremental model divides the project into small, manageable modules (increments), where each increment delivers a fully functional part of the system.

Key Characteristics:

  • The product is built in small, usable portions (increments).
  • Each increment adds new functionality to the previous one.
  • Works well when core requirements are clear, but additional features can be added later.

Phases in Incremental Development:

  1. Requirement Analysis – Define core and future features.
  2. Divide into Increments – Plan features for each release.
  3. Design & Develop Increment – Build one part at a time.
  4. Test & Deploy – Release each increment when ready.

Advantages:

✔ Users get working functionality early.
✔ Easier to test and debug smaller parts.
✔ Lower initial cost compared to full delivery.

Disadvantages:

✖ Requires a clear initial architecture.
✖ Later increments may require changes to earlier ones.

Examples of Incremental Models:

  • Unified Process (UP)
  • Feature-Driven Development (FDD)

3. Iterative vs. Incremental Comparison

Feature Iterative Model Incremental Model
Approach Refines the whole system in cycles Adds features in small parts
Delivery Each iteration improves the entire system Each increment delivers a new feature
Requirements Evolves over time Mostly fixed, but features added later
Best For Unclear or changing requirements Stable core requirements with phased features

4. Combined Models (Iterative + Incremental)

Many modern Agile methodologies (like Scrum) combine both approaches:

  • Iterative → Refining the product over sprints.
  • Incremental → Delivering new features in each release.

Example: Agile Scrum

  • Work is divided into sprints (iterations).
  • Each sprint delivers a potentially shippable increment.

Benefits:

✔ Faster feedback and adaptability.
✔ Continuous improvement.
✔ Reduced risk of project failure.

Conclusion

  • Iterative models focus on refining the product through repeated cycles.
  • Incremental models focus on adding features in small, usable parts.
  • Combining both (as in Agile) provides flexibility and early value delivery.