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System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

What difficulty level is this interview question?

This is a medium difficulty System Design question, commonly asked during Technical Screen rounds at Rippling.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Rippling during technical interviews.

Extend rules for trip-level aggregates and outputs

Q: Extend rules for trip-level aggregates and outputs

This question evaluates a candidate's competency in system design for backend rule engines, covering data aggregation and grouping strategies, rules evaluation and explainability, API/schema design, and performance considerations.

Extend Rules Engine: Aggregate Trip-Level Policies

Context

You previously built an expense policy engine that evaluates per-expense rules (e.g., "a single meal cannot exceed $50"). Extend that system to support aggregate, trip-level rules that operate over groups of expenses for the same trip.

Assume each expense has at least: expenseId, tripId, employeeId, category, amount, currency, incurredAt. Currency normalization to a policy currency (e.g., USD) is available.

Requirements

Add support for aggregate rules including (but not limited to):

A trip’s total expenses cannot exceed $2,000.
Total meal expenses per trip cannot exceed $200.

In the provided sample, trip "002" violates both rules. Update the design and the evaluateRules return type so the output includes per-trip violations alongside per-expense violations.

Describe:

Grouping/aggregation strategy (how expenses are grouped and metrics computed)
Evaluation order (per-expense vs. per-trip and how updates flow)
Explainability for aggregates (what evidence is returned and how it’s human-readable)
Performance considerations (throughput, latency, incremental updates)
How these results integrate into the expenses API used by many companies

Provide:

Updated component design for aggregate rules
A precise return type/schema for evaluateRules that includes per-trip violations
A short, concrete example showing trip "002" violating both aggregates

Context

Assume each expense has at least: expenseId, tripId, employeeId, category, amount, currency, incurredAt. Currency normalization to a policy currency (e.g., USD) is available.

Requirements

Add support for aggregate rules including (but not limited to):

A trip’s total expenses cannot exceed $2,000.

Total meal expenses per trip cannot exceed $200.

In the provided sample, trip "002" violates both rules. Update the design and the evaluateRules return type so the output includes per-trip violations alongside per-expense violations.

Describe:

Grouping/aggregation strategy (how expenses are grouped and metrics computed)

Evaluation order (per-expense vs. per-trip and how updates flow)

Explainability for aggregates (what evidence is returned and how it’s human-readable)

Performance considerations (throughput, latency, incremental updates)

How these results integrate into the expenses API used by many companies

Provide:

Updated component design for aggregate rules

A precise return type/schema for evaluateRules that includes per-trip violations

A short, concrete example showing trip "002" violating both aggregates

Extend rules for trip-level aggregates and outputs

Quick Overview

Extend Rules Engine: Aggregate Trip-Level Policies

Context

Requirements

Solution

Submit Your Answer to Earn 20XP

Extend rules for trip-level aggregates and outputs

Quick Overview

Extend Rules Engine: Aggregate Trip-Level Policies

Context

Requirements

Solution

Submit Your Answer to Earn 20XP