Library Management System — OOD Interview Walkthrough

Phase 1: Requirements & Use Cases

Interviewer: "Design a library management system."

Candidate: "Before I model anything, let me reframe that statement. A library management system is responsible for tracking books, managing member accounts, handling checkouts and returns, enforcing loan rules, processing fines, and supporting catalog search. Is that a fair scope?"

Interviewer: "Yes. Who are the actors?"

Candidate: "I see three primary actors:

1. Member — a registered library patron who searches the catalog, borrows and returns books, makes reservations, and pays fines.
2. Librarian — a staff member who adds and removes books, manages members (block/unblock), and has elevated system access.
3. System — the automated component that triggers overdue notifications, updates book availability when a reservation activates, and auto-calculates fines.

And the core use cases:

1. Search catalog — by title, author, subject, or publication date
2. Checkout a book item — borrow a specific physical copy
3. Return a book item — return it, trigger fine assessment
4. Reserve a book — queue a hold when all copies are checked out
5. Cancel a reservation
6. Renew a loan — extend due date if no pending reservations
7. Pay a fine
8. Add / remove / edit books (Librarian only)
9. Block / unblock a member (Librarian only)"

Interviewer: "Should we support multiple library branches?"

Candidate: "I'd scope that out for this design. Multi-branch introduces distributed inventory, cross-branch transfers, and inter-branch loan policies — a substantial surface that distracts from the core OOD challenge. I'll model a single library with a single physical catalog. If we needed multi-branch…