Functional Notional Syllabus

I would like to ask about the Functional Notional Syllabus but first I can provide you with its definition mentioned by Brown:

A notional-functional syllabus is a way of organizing a language-learning curriculum, rather than a method or an approach to teaching. In a notional-functional syllabus, instruction is not organized in terms of grammatical structure, as had often been done with the Audio-Lingual Method (ALM), but instead in terms of "notions" and "functions."
In this model, a "notion" is a particular context in which people communicate. A "function" is a specific purpose for a speaker in a given context. For example, the "notion," of shopping requires numerous language "functions," such as asking about prices or features of a product and bargaining.
Proponents of the notional-functional syllabus[who?] claimed that it addressed the deficiencies they found in the ALM by helping students develop their ability to effectively communicate in a variety of real-life contexts.

Now, my question is:
how can we differentiate between the "notions" and the "functions"? I mean for example, can I say that "shopping" is the conceptual idea, andn the functions that can be applied in that context are like "bargining, asking about the features of something.." are the "functions"? or I should say that the notion is "bargining" and the differnt ways in asking about prices are the functions?

Many thanks.

DA Wilkins wrote the book Notional Syllabuses, which is central to this. If the notion is thecontext, then bargaining strikes me as not enough in itself to be the notion- it's a strategy used to achieve your aims, and a way in which people communicate but to me not the context.

Re: I'm confused!

Does it mean that Brown's ideas were against Wilkins beliefs?
because I got all what I wrote before from the Wikipedia.

STRATEGY is a key word used by Wilkins, I think.
the term "notional syllabus" embraces the strategy of language teaching that derives the content of learning form an initial analysis of the learner's need to express meaning.

from: The Concise Oxford Dictionary of Linguistics:
notional syllabus. Strategy for teaching a language based on and organized by the functions that utterances can have
but I don't understand this!

Can you provide me with an example: how to differntiate between "notion", and "function"?

Many thanks.