Tim Mitchell has a few tips for managing business logic, particularly when building ETL processes:
First things first: let’s get on the same page with what is meant by business logic. When I refer to business logic (also commonly referred to as business rules), I’m talking about the processing rules that are used to transform an organization’s data so that it is accurate, understandable, and usable. In almost all cases, these business rules are not designed to change the meaning of the data, but to clarify and make it easier to comprehend. Business logic may be applied when data arrives from other sources, or to existing data to reflect changes that have taken place.
Business logic is usually highly customized for and by each organization. The amount of processing required is heavily dependent on factors such as source data quality, reporting granularity, technical skill level of the intended audience, and even company culture.
It’s worth reading the whole thing.