We start from the rough version. You describe the outcome you need, we work out what data it depends on and whether that data exists. If the honest answer is that your question cannot be answered with what is available, you hear it before the budget is committed rather than after.
This work usually arrives late and against a fixed date. A planning window, a grid connection, a funding round, an investor milestone. We scope to that date and deliver in sprints against it, because a piece of analysis that lands after the decision was made is worth nothing regardless of how good it is.
What you get at the end is yours and documented. The database schema and the processing steps, with the reasoning behind the decisions written down. Your people can run it and change it without calling us. We are not trying to become a dependency.