← QCE Digital Solutions Unit 3

Waterfall (sequential) development

A method where each stage (requirements, design, build, test, release) is finished in fixed order before the next starts, with little change once done, so late changes cost more.

Part of: QCE Digital Solutions Unit 3 — Interactions Between Users, Data and Digital Systems — Module 119

Understanding Waterfall (sequential) development in QCE Digital Solutions Unit 3

What it does: The build stage only begins once the design stage is complete, which shows the strict stage-by-stage order of waterfall. A late change means going back and redoing finished work from several stages, so the cost of late changes grows. Waterfall suits projects where the requirements are clear and fixed at the start. Frequent change suits agile methods better. Testing is its own stage that comes after building, so a mistake in the requirements may only be found late.

Common mistakes: The loop must keep finishing stages until release is reached, so the condition should be stage != "release". With == the loop would never run at the start. Waterfall follows a fixed order. After design is approved the next stage is build, not test. Skipping build breaks the sequence.

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Learning

Duo

In waterfall development, which statement is correct?

All stages run at the same time in short cyclesEach stage is finished before the next stage starts

Matches

Build → Design → Requirements → Test → Release

↓

The stages are in the wrong order. Waterfall must run Requirements, then Design, then Build, then Test, then Release.

Applying

Meanings

Term

waterfall development

Meaning

A method where each stage (requirements, design, build, test, release) is finished in fixed order before the next starts, with little change once done, so late changes cost more.

Practice

SET stages TO Requirements, Design, Build, Test, Release

Testing

Gaps

IF THEN

Check Answer

Spots

1stage = "requirements"

2while stage == "release":

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Quick Questions

1. In waterfall development, which statement is correct?

A. Each stage is finished before the next stage starts ✓

B. All stages run at the same time in short cycles

Waterfall is sequential: requirements, design, build, test and release happen in a fixed order, one after the other.

2. Which order shows the stages of waterfall development?

A. Build, release, design, test, requirements

B. Requirements, design, build, test, release ✓

Waterfall flows like a waterfall: you plan the requirements first, then design, build, test and release.

3. A client wants a school canteen app and signs off every requirement before design starts. Which method fits?

A. Waterfall, because the requirements will change every week

B. Waterfall, because the requirements are fixed up front ✓

Waterfall suits projects where the requirements are clear and fixed at the start. Frequent change suits agile methods better.

4. The team has finished the build stage and now wants to change a core requirement. What is likely to happen in waterfall?

A. The change is costly because earlier stages must be redone ✓

B. The change is cheap because waterfall expects constant changes

Late changes cost more in waterfall because design and build work already completed has to be reworked.

5. Which is a feature of waterfall development?

A. Little change is allowed once a stage is complete ✓

B. Users test a new version at the end of every week

Once a stage is signed off, waterfall avoids going back. Weekly versions with user feedback belong to iterative or agile methods.

Match the Pairs

Requirements → Design → Build → Test → Release → The fixed order of waterfall stages, where each stage is finished before the next one starts

requirements_signed_off = True → The requirements are fixed and locked in, so later changes need extra approval and effort

In waterfall, a stage must be finished before the next stage can start → if design_complete: start_build()

A change found late in a waterfall project costs more because earlier finished stages must be redone → change_cost = redo_design + redo_build + retest

Build → Design → Requirements → Test → Release → The stages are in the wrong order. Waterfall must run Requirements, then Design, then Build, then Test, then Release.

Waterfall: change the requirements freely after the Build stage with no extra cost → Waterfall has fixed requirements, so late changes are costly because finished stages must be reworked.

Key Term

waterfall development

A method where each stage (requirements, design, build, test, release) is finished in fixed order before the next starts, with little change once done, so late changes cost more.

Fill in the Blanks

1. stageDone ← TRUE IF stageDone THEN startNextStage()

Hint: Type the variable that records the current stage is finished before the next one can begin.

2. requirementsLocked ← TRUE IF requirementsLocked THEN rejectChange()

Hint: Type the Boolean value that shows the requirements are fixed after sign-off.

3. costEarly ← 100 costLate ← costEarly * 10

Hint: Type the arithmetic operator that makes a late change cost many times more than an early one.

4. FOR stage IN stages complete(stage) signOff(stage)

Hint: Type the keyword that starts a loop going through the stages one at a time, in order.

5. IF changeCost > budget THEN rejectChange() ENDIF

Hint: Type the comparison operator that checks whether a late change costs more than the budget allows.

Spot the Error

Question 1

A stage = "requirements"

B while stage == "release":

C print("Finish", stage)

D stage = next_stage(stage)

Line B — The loop must keep finishing stages until release is reached, so the condition should be stage != "release". With == the loop would never run at the start.

Question 2

A current = "design"

B approved = True

C if approved:

D current = "test"

Line D — Waterfall follows a fixed order. After design is approved the next stage is build, not test. Skipping build breaks the sequence.

Question 3

A change_cost = 1

B for stage in done_stages:

C change_cost /= 2

D print(change_cost)

Line C — In waterfall, each finished stage makes a change more expensive. The cost should grow with *= 2, not shrink with /= 2.

Question 4

A requirements_fixed = False

B if requirements_fixed:

C print("Start design")

D lock_requirements()

Line A — Waterfall needs the requirements finished and fixed before design starts. The flag should be True, otherwise the design stage would never begin.

Question 5

A def finish(stage)

B print(stage, "complete")

C return True

Line A — A Python function definition must end with a colon. It should be def finish(stage):.

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