I've found a similar process by sketching up the domain logic, or typical steps of it, in as high level of pseudo-code as I can. Play around with it to try to o

I've found a similar process by sketching up the domain logic, or typical steps of it, in as high level of pseudo-code as I can. Play around with it to try to optimize (factor) expressiveness. One then starts to see commonalities, and thus a domain-specific language(s) emerges. This language(s) may resemble or even become an API(s). From a different direction, form a relational model, even if not using an RDBMS, to clarify the relationships between the domain parts. Once you do both of these, then a bigger picture starts to form, and you refine it to have the API's work properly from the data relationship perspective.