Construct a problem specification
Construct a problem specification
In this lesson
- Explaining why computer scientists specify a problem before solving it
- Writing a problem statement, constraints and limitations, objectives and goals, input and output specifications, and evaluation criteria
- Telling a strong, specific specification from a weak, vague one
LearnUnderstand the problem first
LearnThe parts of a problem specification
LearnWeak and strong: a customer-service problem
A company wants to improve its customer service. Compare these versions.
| Part | Weak | Strong | Why the strong one works |
|---|---|---|---|
| Problem statement | “Our customer service processes are inefficient.” | “Customers wait an average of 25 minutes on hold before reaching a representative, which has led to a 15 % increase in abandoned calls over the past quarter.” | Focused and measurable; it names the problem (hold times) and its consequence (abandoned calls). |
| Constraint | “We don’t have many resources to fix this.” | “The project budget is limited to $10,000 and cannot be exceeded because of funding restrictions.” | It names the resource, gives an exact figure and says the limit is fixed. |
| Objective and goals | “Make customers happier.” | Objective: “Increase customer satisfaction with service interactions.” Goal: “An average rating of 4 out of 5 on post-service surveys over the next six months.” | The goal is measurable, has a time limit and is linked to the objective. |
LabBuild a specification for a school canteen
First name the part of the specification each statement belongs to. Then compare each part with a weaker version.
Scenario. A school canteen serves 600 students in a 40-minute lunch break. The head of catering asks for an online pre-order system.
Step 1 · Which part of the specification is each statement?
- Each order: the student’s 8-digit ID, 1 to 5 items chosen from that day’s menu, and a collection slot (12:30, 12:45 or 13:00), paid from the student’s canteen account.
- At lunchtime students queue for an average of 18 minutes, so about one in five leave without eating and food prepared for them is thrown away.
- Average queue time measured for two weeks before and after launch; at least 90 % of orders ready at the chosen slot; an average rating of at least 4 out of 5 in a student survey.
- The system must be in use by 1 March, cost less than €4,000, and run on the canteen’s existing tablets and the school’s student accounts.
- A confirmation with a collection number shown to the student, and a list of orders for each collection slot printed for the kitchen by 11:00.
- Reduce queuing at lunchtime: cut the average queue time to under 5 minutes, and food waste by 30 %, within the first term.
Name all six parts correctly, then choose the stronger version of each part, to complete this activity.
CheckObjective or goal?
A school library is planning a new catalogue system. Classify each statement.
- Encourage students to read more for pleasure
- Increase fiction loans per student by 25 % by the end of the school year
- Make it easier for students to find the books they want
- Reduce the average time to find a book on the shelves to under 2 minutes by January
CheckWhat kind of constraint?
A team is building an app for a school’s coursework submissions. Classify each constraint.
- The total budget is £3,000
- Two developers are available for six weeks
- The app must run on the school’s existing Android tablets
- Students’ personal data must be handled according to data protection law
- Coursework must be submitted and authenticated according to the exam board’s regulations
LearnInputs, outputs and evaluation: a customer-service chatbot
A company builds a chatbot that answers customers’ questions written in everyday language.
CheckMatch each evaluation factor to the question it answers
Select a term on the left, then its description on the right.
CheckQuick check
A bus company asks for help with route 12. Which is the best problem statement?
ExamWorked exam answer
A public library loses many books because borrowers forget to return them; it currently sends no reminders. The librarian asks for a system that reminds borrowers. Construct a problem specification for this system.
[6]ReviewMistakes examiners see
Writing a solution as the problem statement (“the library needs an app”). State what is wrong and why it matters.
Goals that cannot be measured (“make it better”) or have no time limit. A goal needs a number and a deadline.
Input specifications that only say “the user’s details”. Give each item, its format or type and its allowed values.
Use the figures given in the scenario. Specific, measurable statements earn the marks.
Exam practiceExam-style questions
5 questions · 15 marks. Answer each one first, then mark it yourself against the markscheme. Your answers are saved in this browser only.
Riverside Sports Centre has eight tennis courts. Members can book courts only by phoning reception, which is staffed from 09:00 to 17:00. Over the last three months, 15 % of booked court hours were not used because members did not turn up, and 60 members cancelled their membership, many saying booking was too difficult. The manager wants a system that lets members book and cancel courts online. The project has a budget of £6,000, must be ready before the summer season starts in 10 weeks, and must use the centre’s existing membership database. Courts are booked in one-hour slots from 07:00 to 22:00, up to 14 days ahead.
Identify one resource constraint and one technical constraint for this project.
Construct a problem statement for this project.
Construct one high-level objective for the system and two specific goals linked to it.
Outline the input specification for a single court booking.
Apart from effectiveness, explain two evaluation criteria the manager could use to judge whether the system is successful.
0 of 5 questions marked. Mark every question to see your total.
Exam-style questions written for Praxis IB in the format of the 2027 specimen papers. They are not IB past-paper questions.