Unify behavior, billing, and CRM data

WHAT THIS TESTS The interviewer wants a data-engineering architecture plus awareness of the hard parts. Joining behavioral, billing, and CRM data sounds simple until you confront that none of the systems share a clean key and each emits data at a different rate and grain.

A GOOD ANSWER COVERS Use an ELT pattern into a central warehouse. Front-end behavior streams in as events through a collector; Stripe and Salesforce are synced by scheduled batch or change-data-capture, landing raw, then transformed in the warehouse. The crux is identity resolution: an anonymous visitor has a device or session id, a paying user has a Stripe customer id, and a sales lead has a Salesforce id, often with different emails. You need an identity-stitching layer that resolves all of these to one canonical customer, including bridging the anonymous-to-known transition at signup. On top, model the metrics: activation from events, conversion joining behavior to first paid subscription, revenue from Stripe. Key challenges to name: identity stitching, schema drift as third-party APIs change fields, differing data freshness and grain between a real-time event and a daily CRM sync, late-arriving data, and PII governance and access control across systems.

COMMON WRONG ANSWERS Assuming all three systems share a join key like email. Ignoring the anonymous-to-known stitching problem, so pre-signup behavior never links to revenue. Forgetting schema drift and the data-freshness mismatch. Overlooking PII compliance.

LIKELY FOLLOW-UPS How do you stitch an anonymous session to a user after signup? How do you handle Salesforce changing a field name? Batch versus streaming for the CRM source?

ONE CONCRETE EXAMPLE A visitor browses anonymously with a session id, signs up generating a user id, later becomes a Stripe customer, and is logged as a Salesforce opportunity. Your identity-resolution layer links session, user, Stripe, and Salesforce ids into one customer record. Now you can attribute that closed-won revenue back to the original GTM campaign that drove the anonymous visit, the unified view leadership wanted.