[OSM-talk] empty relations

[Frederik Ramm]

Hi,

> Ok, so it is basically (ab)using the only locationless entity available 
> in OSM model to store some data,  which _may_ be referenced by other
> relations. It is still not clear to me how could one reference it 
> without having it retrieved in some bbox.

You could retrieve it by id, by a search request through one of its 
tags, from a change file/planet dump, or you could not have retrieved it 
because you created it together with the object referencing it.

> Why not store the data about the company in that latter, second 
> relation, and using this same relation to group all the roads operated 
> by a particular company at the same time?

Possible, but only for those cases where an entity exists only in one 
role globally, i.e. entity X only ever operates roads. If entity X was 
to take part in another role in another relation (e.g. it not only 
operates roads but it could also be the owner of a building or whatever) 
then your approach would duplicate information about X.

> Is it just a bad example or I misunderstood it somehow? Are there any 
> other, meaningful uses?

It is not a bad example and you understood it correctly.

All this is highly theoretical anyway but at least there are these 
options and if someone comes up with some clever use for them then he 
has the freedom to do it.

>> The feature is not used yet but why disable it if it doesn't hurt.

> We could just as well just deprecated segments, but decision was to 
> ditch them completely. Now we find ourselves splitting ways into chunks 
> no longer than a segment and gluing them together with relations (way 
> has to be split whenever there is a bridge, speed limit change, bus or 
> cycle route joins the way...). This might be a bit radical, but we could 
> as well ditch ways and replace them with relations (of ordered nodes to 
> compose ways). </thinking aloud>

We could do all sorts of things but this has nothing to do with your 
original question.

> But it doesn't make non-referenced relations with no members any more 
> useful.

Then don't use them.

Bye
Frederik