ETL & ELT
Where transformation runs and what that decides. Not a fashion — a question about where compute lives, how much raw history you keep, and what you can reprocess after you find a bug.
Extract, transform, load. The destination only ever sees rows that already conform — a real guarantee for its readers, bought with the original that nobody kept.
Extract, load, transform. The destination holds the raw copy and does the work — which turns most transformation bugs into a re-run and hands the destination every obligation the raw data carries.
Two orderings, six criteria. Where compute is available, how large raw is, whether you need history, what security forbids, how complex the logic is, and what the destination can actually do.
In the source, in a dedicated cluster, in the warehouse, in the query at read time, or in the BI tool. Each placement moves cost, freshness, testability and governance somewhere different.
Three jobs that need separating — preserve what arrived, make it usable, model it for consumers. The names vary by house; the purposes do not.
Bronze, silver, gold is a widely used set of names for raw, staging and curated. It is a convention, not a requirement, and it is not an architecture.
An immutable copy of what arrived is what makes every downstream mistake fixable. It is also the most sensitive dataset the platform holds. Both are true and neither cancels the other.