or to have both problem and solution objects with ways to compute the latter from the former. problem domain objects are often part of the input and internal c

or to have both problem and solution objects with ways to compute the latter from the former. problem domain objects are often part of the input and internal computation space, whereas solution objects are usually user-friendly world views. so both are helpful to think about before writing too much code. in the financial transaction example, input and computations occur over transaction objects. however users want to navigate monthly balances. thus, there has to be a cross reference or object transformation from the highly granular transactions to monthly aggregations.