Asset Partition Mapping

An asset partition mapping states which upstream partitions are required for a downstream partition. It describes dependency scope, not a file layout or a guarantee that the required input exists.

A daily total can depend on the same date’s rows. A trailing seven-day total needs that date and the six preceding dates. Rebuilding only the output date as input changes the latter calculation.

Declare the mapping when partition schemes differ, and check boundaries, time zones, missing history, and corrections. An orchestrator can plan work from declared dependencies; it cannot recreate unavailable input versions or infer every undeclared dependency.

Partition replay still needs stable input identity and safe destination writes. A partition key can be reused while its source data changes, so it should not be mistaken for an immutable snapshot identifier.

For an output dated October 7, a trailing seven-day mapping reads October 1–7. A correction to October 2 can affect outputs October 2–8. This reverse traversal finds what to rebuild; it is broader than the corrected input date. Restrict execution to the intended output range and account for missing prior history explicitly.

See Asset-Oriented Orchestration: Dagster and Prefect for worked examples.

Further reading

• Dagster: Defining dependencies between partitioned assets