What exactly consists of 'Business Logic' in an application?

Question

I have heard umpteen times that we \'should not mix business logic with other code\' or statements like that. I think every single code I write (processing steps I mean) con

Answer 1

Business logic is pure abstraction, it exists independent of the materialization/visualization of the data in front of your user, and independent of the persistence of the underlying data.

For example, in Tax Preparation software, one responsibility of the business logic classes would computation of tax owed. They would not be responsible for displaying reports or saving and retrieving a tax return.

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@Lars, "services" implies a certain architecture.