[Taginfo-dev] Feature request, might solve a small bit of the xapi-problem

[Jochen Topf]

On Sun, Jul 17, 2011 at 08:43:03PM +0200, Gorm E. Johnsen wrote:
> Suggested feature:
> That each key/value combination remembers one (or a few?) of the relevant
> osm-object-ids.
> That way we could link directly to the map, object info page and
> remote-control for those objects, completely bypassing xapi.
> 
> Why?
> 3/4 of the unique values of the highway tag has three or less occurrences.
> Most are mistakes, mis-spellings and other errors.
> Some of the values legal in the db is really difficult or impossible to
> search for in xapi.
>  - try searching for highway=highway=service... or other strange
> combinations

Not a bad idea. Lets look at the numbers:

There are currently about 60 million different tags. If we store one node id
(64bit), and one way and relation id (each with 32bit) that would need about
one extra GB of RAM. We could also just store one 64bit id and encode the
type in the first two bits, that way we would only need 8 bytes per tag, or
about 500 MB alltogether. If we store more IDs it will obviously need more.

So just looking at the memory requirement it could be done I think. But I
am a bit reluctant, because it would expand the "job" of Taginfo further
than it should be. I'd rather have a better XAPI or other other service I
could link to. Then everybody can concentrate on improving one tool with
one job and you'll get something much more flexible. Lately a lot of people
have been experimenting with new and different XAPI implementations, so
I hope this issue will be resolved at some point.

The other problem I see is the usability issue. Its difficult to make it
clear to the user why the id is sometimes available and sometimes not (or
only one basically arbitrary id is available and not others).

Maybe the solution would be to not add this function to Taginfo itself, but
create a new service that is not as powerful as XAPI (and therefore not as
slow) but can do this (and maybe a few other things that Taginfo users need).

Jochen
-- 
Jochen Topf  jochen at remote.org  http://www.remote.org/jochen/  +49-721-388298