How to distinguish business logic from functional logic in software?

Business logic refers to the rules and processes that reflect the specifics of the subject area and determine how the system should operate from a business perspective. It answers the questions "what" and "why": for example, how to calculate a discount, how to process orders, what conditions must be met to perform an operation.

Functional logic (or technical logic) is the implementation of specific functions and operations necessary for the program's operation but not directly related to business rules. This includes, for example, working with a database, validating data formats, interacting with external services.

Example:

• Business logic: "If the order amount exceeds 1000, apply a 10% discount"
• Functional logic: "Calculate the order amount, save data to the database, send a notification"

Thus, business logic can be separated in terms of meaning — it describes the rules and processes of the subject area, while functional logic involves technical steps to implement these rules.