Design a rare-book lending and returns system

Q: Design a rare-book lending and returns system

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Question

System Design: Rare Books Circulation Across Multiple Branches

Context

Design a system to manage borrowing and returning rare books across multiple library branches. Rare items have special handling (limited copies, in-library-only policies, appointments, inspections) and strong compliance needs (tamper-evident audit trails). The system must prevent double-booking the same copy and scale to many branches and users.

Requirements

Functional Requirements

Catalog & Discovery
1. Full-text search and faceted browse across titles, authors, subjects, branches, availability.
2. Variant records: title-level records and copy-level metadata (condition, restrictions, branch location).
Reservations & Access 3. Place/modify/cancel holds at title level; assign to a copy when actionable (e.g., appointment confirmed). 4. Waitlists with fair ordering and promotion rules; expiration of offers. 5. Appointment-based access for reading rooms; time-slot scheduling and capacity limits per branch. 6. Policy enforcement: in-library-only vs. loanable; max loan periods; user eligibility; fines.
Identity & Staff Controls 7. Identity verification (membership, ID verification at branch) and digital consent/signature capture. 8. Staff overrides (break-glass) with reason codes and elevated auditing.
Circulation & Integrity 9. RFID/barcode check-in/out; gate integration for in-library-only items. 10. Condition inspection at check-out/check-in with photos, notes, and damage codes. 11. Chain-of-custody and tamper-evident audit logs for all custody transitions. 12. Fines for late/damaged/lost items; incident reports for disputes. 13. Inventory reconciliation: periodic RFID sweeps, discrepancy reporting, cycle counts.

APIs (examples)

Users: create/update user; verify identity; attach credentials.
Holds: place/modify/cancel hold; list user holds; accept/decline offer.
Appointments: create/modify/cancel; check availability.
Circulation: check out; check in; transfer between branches; mark in-reading-room custody.
Condition/Incidents: report damage/loss; upload inspection photos; file incident.
Admin/Staff: staff override action; reconcile inventory; manage policies.

Data Model (high level)

Users, Items (title-level), Copies (physical holdings), Policies, Holds, Appointments, Transactions (circulation), Fines, Incidents, Audits (append-only), Media (photos).

Consistency & Transactions

Prevent double-booking limited copies and time slots.
Atomic state transitions for holds, appointments, and check-out/check-in.
Idempotent APIs to handle retries.

Architecture

Services: Catalog/Search, Reservations, Appointments, Circulation, Identity & AuthZ, Policies, Audit/Compliance, Notifications, Media, RFID/Edge Gateway.
Data stores: relational DB for core transactions; search index; cache; queues; object storage; WORM/append-only audit store.
Security: strong authorization, encryption at rest/in transit, tamper-evident audits.

Non-Functional & Operations

Scale assumptions; expected read/write QPS; handling hot titles.
Concurrency control; failure handling; background jobs; notifications.
SLA/SLO, RTO/RPO; monitoring & alerting.
Cost trade-offs.
Extensions: inter-library loans; offline branch operations.