I can't share everything here, but basics are this. Three tables: accounts, transactions, entries. Entries have amount, unit, notes. Accounts have name, parent_account. Transactions have subject, notes, date. That's the data. Then I have a view that flattens accounts tree, so that each has name and fullname. Name being Fun, fullname a full path to that account, eg. Expenses:Fun.

With that base structure, you can start answering any questions by just summing entries groupped by accounts filtered by a regexp on fullname and fitler on date. What is my cashflow for any time period, what is my equity, what is my balance sheet, what I actually have, what changed recently, how any of this develops over time...