4. Distinguish the type of function

With a little common sense, you've found the service functions and the technical functions.

But you want to find all the functions without forgetting any, and use standardization.

You'll need to classify and order the functions, then characterize them, and finally prioritize them. But there are two types of service function (SF). You need to distinguish between them, and use standardization to express them.

If you're using commercially-available software, you'll need to follow certain rules, starting with function research and studying the relationships between the product or system and its environment.