An explanation links a design choice to a user need. Use a four-link chain: the choice, the need, the principle and the trade-off.
This lesson is part of human computer interaction. It builds on the criteria in evaluating clarity, feedback and navigation.
What is the four-link chain?
| Link | Question it answers | Sample wording |
|---|---|---|
| Choice | What was decided? | “The app asks for confirmation before deleting.” |
| Need | What does the user need? | “A user may tap delete by accident.” |
| Principle | Which idea supports it? | “This gives feedback and protects against errors.” |
| Trade-off | What does it cost? | “It adds one extra tap.” |
You do not always need all four. A short-mark answer uses the first three in one sentence, and a longer answer adds the trade-off.
Worked example: a delete confirmation
A fictional notes app lets a student delete a saved note. The design shows a box: “Delete this note? It cannot be undone. Cancel / Delete.”
A weak answer says: “The app has a confirmation box.” It names the choice only, with no reason.
A strong answer reads: “The app asks for confirmation before deleting because a student might tap Delete by accident and lose work. This protects against errors and gives the user a chance to change their mind. The cost is one extra tap.”
The strong answer contains the choice, the need, the principle and the trade-off.
What do markers look for?
A marker looks for a reason linked to the situation in the question. A reason that would fit any app is weaker than one that uses the details given.
For example, “it makes the app better” fits everything and earns nothing. “Because the note cannot be recovered” is specific to a delete action.
A second example: two correct decisions
A school contact form needs a student’s class. Two designs are possible.
- A dropdown of class names. It prevents typing errors and makes every entry match the school’s list. The trade-off is that a long list takes time to scan.
- A free text box. It is fast for the user who knows the class. The trade-off is that spelling differences, such as “4 Bestari” and “4bestari,” create errors.
Either choice can earn full marks when the reason fits the situation and the trade-off is named.
Check yourself
A fictional bus app shows the next bus time in large text on the first screen, and moves the route map to a second screen. Explain this decision in two or three sentences.
Answer
A model answer: “The app puts the next bus time on the first screen because users open it to answer one question: when does the bus arrive? Showing it straight away reduces the taps needed and supports a quick task. The trade-off is that the route map takes an extra step to reach.”
It has the choice, the need, the principle of a quick, simple task, and the trade-off.
What to study next
Explanations also help when you test a design. Continue with testing a prototype with observable tasks, then use the practice set.
Note your thin answers in the mistake log. If you want a teacher to question your reasons, see online one-to-one Computer Science tuition.