Design Expense Management - System Design | WinJob

Problem Statement & Context

Corporate expense platforms reconcile employee spend with finance controls: capture receipts, extract structured fields, enforce policy (per diem, category caps, receipt required), route approvals, and export to ERP/payroll. Unlike a shopping cart, the hard part is messy unstructured input (photos, forwarded emails, card feeds) converging on auditable numbers.

Personas

Employee: snap receipts, mileage, corporate card auto-match
Manager: approve exceptions, bulk actions at month-end
Finance: audit trail, tax tags, GL coding, reimbursement batches

Scale anchors (state explicitly)

Assume 80k enterprise tenants, 12M active employees, 180M expense lines/month, 2.3 receipts/line average. Peak month-end close = 4× daily submit rate for 72 hours. Target: receipt upload ack < 300ms, OCR enrichment p95 < 45s, approval API p99 < 250ms.

Core tension

report_id must serialize workflow transitions while OCR workers mutate line items asynchronously. Finance needs strong audit; employees need offline-friendly capture.

javaOne Dark Pro

1 public final class ReportSubmitService {
2   public SubmitResult submit(UUID reportId, String idempotencyKey) {
3     return txTemplate.execute(status -> {
4       var report = reports.lockForUpdate(reportId);
5       var violations = policyEngine.evaluate(report);
6       if (violations.stream().anyMatch(Violation::blocking)) {
7         throw new PolicyViolationException(violations);
8       }
9       audit.append(reportId, "submitted");
10       outbox.enqueueExport(reportId);
11       return SubmitResult.ok(report.version());
12     });
13   }
14 }

Section 1 focus

Interviewers expect Problem Statement & Context to cite report_id consistency, OCR confidence gating, and SOX-friendly audit — not generic microservices buzzwords.

Why interviewers care

Expense Management interviews reward crisp scope, explicit trade-offs, and failure stories—not generic microservice diagrams.

Interview checkpoint

Name one failure story for Problem Statement & Context that proves you understand real outages, not happy-path diagrams.

Key Highlights

•Problem Statement & Context: anchor on report_id workflow stickiness
•OCR async; policy blocks on submit
•Immutable receipt blobs + audit hash chain
•Phase understanding checkpoint for design-expense-management

1	public final class ReportSubmitService {
2	public SubmitResult submit(UUID reportId, String idempotencyKey) {
3	return txTemplate.execute(status -> {
4	var report = reports.lockForUpdate(reportId);
5	var violations = policyEngine.evaluate(report);
6	if (violations.stream().anyMatch(Violation::blocking)) {
7	throw new PolicyViolationException(violations);
8	}
9	audit.append(reportId, "submitted");
10	outbox.enqueueExport(reportId);
11	return SubmitResult.ok(report.version());
12	});
13	}
14	}