Yes, sort of rules engine like that is really nice when you have a hodgepodge of data and purposes for it: e.g. your users may supply names, countries, ID numbe

Yes, sort of rules engine like that is really nice when you have a hodgepodge of data and purposes for it: e.g. your users may supply names, countries, ID numbers, various documents, addresses, etc — often with branching flows. (If the user is a business you collect different information than if the user is investing through an IRA or investing individually. The ID verification process wants the front and back of the document if it's a US driver's license, but it is okay with the front only if the document is a passport.) At some point, you have partial answers for everything, depending on what flows users have gone through, in what order, and what the validation requirements of those forms were at that time. Logic engines can answer questions like: Do we need to ask the user for more info for the Invest In XYZ flow? If so, which forms will supply the needed information?