uml - Functional decomposition vs use case

Question

Functional decomposition is not used when applied to use case modeling.

This phrase is a copied one from a question paper.What is the meaning of that phrase.

This is not equal to the question What is Functional Decomposition?

Answer 1

Use cases deal with synthesizing functions, not decomposing them. A technician decomposes a system to find the pieces it is built of. A business analyst tries to stack single parts of a system on piles so they are formed around a single goal. A use case describes a unique single piece of added value a systems gives to an actor. Indeed, functional decomposition is what most people try when describing use cases: finding bits and pieces. They all (like me) come from the programming guild where this is the daily job. But UC synthesis is working the exact opposite!

I recommend reading Bittner/Spence who explain this very complex approach in detail and very nicely.