Iterative and incremental model in Software Engineering - Step-by-Step Execution

Concept Flow - Iterative and incremental model

Start Project

↓

Plan Iteration 1

↓

Develop Increment 1

↓

Test Increment 1

↓

Review & Feedback

↓

Is Project Complete?

No→Plan Next Iteration

↓

Develop Increment 2

↓

Deliver Final Product

The model repeats cycles of planning, developing, testing, and reviewing small parts (increments) until the full product is complete.

Execution Sample

Software Engineering

Iteration 1: Plan -> Develop -> Test -> Review
Iteration 2: Plan -> Develop -> Test -> Review
...
Repeat until complete

Shows how each iteration plans, builds, tests, and reviews a small part of the project.

Analysis Table

Iteration	Phase	Action	Output	Next Step
1	Plan	Define goals for first increment	Plan document for increment 1	Develop
1	Develop	Build first increment features	Working increment 1	Test
1	Test	Test increment 1 features	Test results and bug list	Review
1	Review	Gather feedback and decide next steps	Feedback report	Is project complete? No
2	Plan	Define goals for second increment	Plan document for increment 2	Develop
2	Develop	Build second increment features	Working increment 2	Test
2	Test	Test increment 2 features	Test results and bug list	Review
2	Review	Gather feedback and decide next steps	Feedback report	Is project complete? Yes
-	-	-	-	Deliver final product

💡 Project complete after iteration 2, final product delivered.

State Tracker

Variable	Start	After Iteration 1	After Iteration 2	Final
Plan Document	None	Plan for increment 1	Plan for increment 2	Complete plan
Working Increment	None	Increment 1 built	Increment 2 built	Full product built
Test Results	None	Tested increment 1	Tested increment 2	All increments tested
Feedback	None	Feedback after iteration 1	Feedback after iteration 2	Final feedback incorporated

Key Insights - 3 Insights

Why do we repeat planning in each iteration instead of planning everything at once?

Because each iteration focuses on a small part, planning is done incrementally to adapt to feedback and changes, as shown in the execution_table rows for 'Plan' phase in each iteration.

How does testing after each increment help the project?

Testing early and often finds problems sooner, making fixes easier and improving quality, as seen in the 'Test' phase outputs in the execution_table.

What happens if the project is not complete after an iteration?

The model loops back to plan the next increment, continuing development until all parts are done, shown by the 'Is project complete? No' decision leading back to planning.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after the 'Develop' phase in iteration 1?

A Working increment 1

B Plan document for increment 1

C Test results and bug list

D Feedback report

💡 Hint

Check the row where Iteration is 1 and Phase is 'Develop' in the execution_table.

At which iteration does the project become complete according to the execution_table?

A Iteration 1

B Iteration 2

C Iteration 3

D Never

💡 Hint

Look at the 'Review' phase rows and the 'Is project complete?' column in the execution_table.

If feedback after iteration 1 was ignored, how would the variable 'Feedback' change in variable_tracker?

A It would still show 'Feedback after iteration 1'

B It would jump directly to 'Final feedback incorporated'

C It would remain 'None' after iteration 1

D It would be empty after iteration 2

💡 Hint

Check how 'Feedback' changes after each iteration in variable_tracker.

Concept Snapshot

Iterative and Incremental Model:
- Develop software in small parts called increments.
- Each iteration includes planning, development, testing, and review.
- Feedback after each iteration guides next steps.
- Repeat until the full product is complete.
- Helps manage risks and adapt to changes early.

Full Transcript

The Iterative and Incremental Model breaks down software development into repeated cycles called iterations. Each iteration plans, builds, tests, and reviews a small part of the project called an increment. After each iteration, feedback is gathered to improve the next increment. This cycle repeats until the entire product is complete. This approach helps catch problems early, adapt to changes, and deliver working software faster. The execution table shows each phase per iteration and the outputs produced. Variables like plan documents, working increments, test results, and feedback evolve step-by-step through the iterations. Key moments include understanding why planning repeats, the importance of testing each increment, and how the model loops until completion. The visual quiz tests understanding of outputs at each phase, when the project completes, and the role of feedback. Overall, this model supports flexible and manageable software development.

Practice

1. What is the main idea behind the iterative and incremental model in software development?

easy

A. Skipping testing until the final product is complete

B. Writing all code at once before testing

C. Building software in small parts, adding features step-by-step

D. Developing software without any planning

Solution

1. Step 1: Understand the model's approach

   The iterative and incremental model focuses on building software in small parts, called increments, rather than all at once.

2. Step 2: Identify the key benefit

   Each increment adds new features and improves the product gradually, allowing for early testing and feedback.

3. Final Answer:

   Building software in small parts, adding features step-by-step -> Option C

4. Quick Check:

   Iterative and incremental = small parts + step-by-step [OK]

Hint: Think: build bit by bit, not all at once [OK]

Common Mistakes:

• Confusing it with big bang development
• Thinking testing happens only at the end
• Assuming no planning is involved

2. Which of the following is the correct sequence in the iterative and incremental model?

easy

A. Build -> Plan -> Test -> Design -> Repeat

B. Plan -> Design -> Build -> Test -> Repeat

C. Test -> Build -> Plan -> Design -> Repeat

D. Design -> Test -> Plan -> Build -> Repeat

Solution

1. Step 1: Recall the iterative cycle steps

   The model follows a cycle of planning, designing, building, and testing in each iteration.

2. Step 2: Confirm the correct order

   After testing, the cycle repeats to add more features or improvements.

3. Final Answer:

   Plan -> Design -> Build -> Test -> Repeat -> Option B

4. Quick Check:

   Plan, design, build, test, repeat = correct cycle [OK]

Hint: Remember: plan before you build, then test [OK]

Common Mistakes:

• Mixing up the order of steps
• Thinking testing comes before building
• Skipping planning phase

3. Consider this scenario: A team uses the iterative and incremental model and completes 3 iterations. Each iteration adds 2 features. How many features are added after 3 iterations?

medium

A. 6

B. 3

C. 5

D. 2

Solution

1. Step 1: Identify features added per iteration

   Each iteration adds 2 features.

2. Step 2: Calculate total features after 3 iterations

   Total features = 3 iterations x 2 features = 6 features.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   3 x 2 = 6 features [OK]

Hint: Multiply iterations by features per iteration [OK]

Common Mistakes:

• Adding instead of multiplying
• Confusing iterations with features
• Ignoring incremental nature

4. A team following the iterative and incremental model forgot to test their software after each iteration. What is the likely problem caused by this mistake?

medium

A. Accumulation of undetected errors

B. Reduced development cost

C. Better planning for next iteration

D. Faster delivery of software

Solution

1. Step 1: Understand the role of testing in iterations

   Testing after each iteration helps find and fix errors early.

2. Step 2: Identify consequence of skipping testing

   Without testing, errors accumulate and become harder to fix later.

3. Final Answer:

   Accumulation of undetected errors -> Option A

4. Quick Check:

   Skipping tests = more hidden errors [OK]

Hint: Test each step to catch errors early [OK]

Common Mistakes:

• Assuming skipping tests speeds up delivery
• Thinking planning improves without testing
• Believing cost always reduces without testing

5. A software project uses the iterative and incremental model. After 4 iterations, the team realizes a major feature needs redesign. What is the best approach to handle this using the model?

hard

A. Discard all previous work and start over

B. Complete all planned features before redesigning

C. Ignore the redesign and continue as planned

D. Add redesign tasks in the next iterations and improve gradually

Solution

1. Step 1: Recall flexibility of iterative and incremental model

   This model allows changes and improvements in later iterations without starting over.

2. Step 2: Choose the approach that fits model principles

   Adding redesign tasks in upcoming iterations lets the team improve gradually while delivering working software.

3. Final Answer:

   Add redesign tasks in the next iterations and improve gradually -> Option D

4. Quick Check:

   Model supports gradual improvements and changes [OK]

Hint: Use next iterations to improve and fix features [OK]

Common Mistakes:

• Thinking you must start over for changes
• Ignoring needed redesigns
• Delaying redesign until all features finish