Three words that engineers use interchangeably and shouldn't: Migration is a one-time move — different system, different schema, run once, archive the scripts. Conversion is what happens inside a migration when the shape of the data has to change (types, keys, business rules). ETL is a continuous integration pattern — extract, transform, load — running forever between two systems that both stay alive. This post is about how I've done all three, in real projects, across two eras of...