Design an Online Exam Portal

Problem Statement

Design a simple online exam portal for your college. Features needed: - Students log in and take a multiple choice exam - Each exam has a time limit (e.g. 30 minutes) - Results are shown immediately after submission - Teachers can see all student scores Write your design covering: 1. Database schema (tables for users, exams, questions, submissions) 2. How do you enforce the time limit? 3. How do you prevent students from seeing each other's answers? 4. How is the score calculated automatically? 5. What would break if 500 students take the exam at the same time?

Sample Data

No code required — write your design as text or pseudo-code.
Think about:
- What data needs to be stored
- What happens step by step when a student submits
- What the teacher's view looks like

Expected Output

Schema: users, exams, questions, student_answers tables
Time limit: store start_time, check elapsed on submit
Security: each student only queries their own answers
Auto score: compare student answers to correct_answer column
Scale concern: DB writes spike, consider queuing submissions