Original practice scenario inspired by SAP SE's public business context; this is not a reported interview question or a description of its internal systems. A fictional enterprise report stores orders and customer-segment history with valid_from and valid_to. Explain a temporal join that assigns the segment valid when each order was placed, including missing or overlapping history.
Read model answer +
Use an explicit validity interval at the order timestamp, rather than joining every order to the customer's current segment. Treat overlapping history as a data-quality error, not an arbitrary winning row.
Work through it
Adopt half-open intervals: valid_from <= order_time and order_time < valid_to, with a documented representation for an open-ended interval.
Left join history using customer identity and interval predicates. Preserve orders without a matching segment and label their segment unknown.
Check that each order matches at most one history row. Test exact boundary timestamps, late backfills, gaps, and overlapping versions before aggregating revenue by segment.
Tradeoffs to discuss
Correcting historical validity can change earlier reports. Versioned snapshots or report run metadata help explain those revisions.
Common pitfalls
A WHERE condition on history can drop unmatched orders.
Ranking overlapping matches hides contradictory history instead of resolving its cause.
Original practice scenario inspired by SAP SE's public business context; this is not a reported interview question or a description of its internal systems. A fictional enterprise application exposes an extension callback to customer plugins. You need to add an optional field and later change a required validation rule. How would you release both changes without assuming every plugin upgrades immediately?
Read model answer +
Treat the callback payload and its behavioral guarantees as a versioned contract. Adding data and changing required behavior have different compatibility risks, even when both fit in the same JSON object.
Work through it
Document required fields, unknown-field behavior, error semantics, and supported versions. Add contract fixtures for old and new plugin consumers.
Introduce the optional field with safe defaults and observe compatibility before enabling it broadly. Avoid requiring consumers to enumerate an exact closed field set unless promised.
Release the validation change behind a new contract version or explicit capability negotiation, with migration diagnostics and a deprecation window.
Tradeoffs to discuss
Supporting versions increases maintenance, but forcing a synchronized upgrade across independently managed plugins creates operational risk.
