Reject source schema drift before materializing the mart
A partner renamed subscription_id and the daily transformation published an empty table successfully.
- Focused work estimate
- 1h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Data contracts · Schema evolution
Estimated field mix
- Data engineering70%
- Quality engineering30%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional SaaS analyst reports expansion revenue differently from finance because snapshots, refunds and contract changes are joined at incompatible grains.
Setup prerequisites
- Create a synthetic source schema and local transformation project.
- Use integer minor units and distinct reporting currencies.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Validate required columns and accepted types.
- Fail before replacing the active reporting relation.
- Report the missing contract field and source version.
Implementation constraints
- Avoid relying on a row-count check alone.
Verification to include
- Transform a valid empty source under its declared contract.
- Rename a required column and retain the previous active mart.
Deliverables
- Source contract gate
Rollout and recovery
Run the contract gate before scheduled builds; keep prior output on failure.
Value of the work
For the engineer: Practice analytical modeling and explainable transformation contracts.
For the team: Review trustworthy reporting definitions and the cost of correcting historical reports.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.