[Tagging] Discussion about Multivalued Keys

[althio]

> Thanks for getting this discussion started.

I agree, thank you Colin
Colin, Matthijs, good luck on this one, I hope something will come out
positively.


> One thing to take into account in this discussion is that multi-valued
> keys often move the problem to the data consumer. For that reason I'd
> recommend to avoid them in many cases.

Well in some cases they ought to be useful so let us find a way to
reduce fragmentation.


> Take for example your example shop=supermarket, shop=bakery.
> Independent of the exact way of tagging, using a multivalued tagging
> scheme forces the renderer to make a decision between a supermarket
> and a bakery icon.

So be it. Any data consumer can choose, what is wrong with that?
(May I remind you some data consumer are not rendering data?)
If you want a map/app/analysis/search/navigation on supermarkets, you have it.
If you want a map/app/analysis/search/navigation on bakeries, you have it too.

If you want a generic map/app/analysis/search, you can keep both.
Display 2 results, count 2 instances, render 2 icons.


> Basically, there is no possible way for the
> renderer to support a multi-valued key here!

It is more difficult, I would agree, but "no possible way" looks like
an overstatement.
Really.

> The renderer might have a
> rule that considers supermarkers always more important than bakeries,
> or vice versa. But I think it's much more useful if the mapper decides
> what's the main function, supermarket or bakery, rather than forcing
> the renderer to make a choice.

If possible, the mapper should choose the main function, or make 2
nodes, or whatever.
And now, let us discuss what if not.
I think it would be nice if the renderer was not forcing the mapper to
make a choice when there is none.