[Tagging] Permanent IDs RFC (was part_of:wikidata)

Kevin Kenny kevin.b.kenny+osm at gmail.com
Thu Nov 30 22:14:44 UTC 2017

On Thu, Nov 30, 2017 at 2:30 PM, Yuri Astrakhan <yuriastrakhan at gmail.com> wrote:
> Erkin, the whole idea of the permanent ID is for it to always point to the
> same "conceptual" object. If I create a road, and use an ID for that road
> somewhere, I would like that ID to continue working even if the road gets
> broken up into multiple segments.  I am not exactly sure how your approach
> would solve that.

I really favour a "good enough" solution over a "perfect" one.

The existing wikidata=* scheme is 'pretty good' in that while it won't do things
like "search for all public art works by a given artist", it will
allow backlinking
to specific objects in OSM by means of an Overpass query.

Few mappers, when casually splitting a way, simply delete tags willy-nilly.
Moreover, most way splitting happens in order to do things like add part of
the way to a route relation, put a traffic restriction on part of the
way, or other
things that don't change the 'identity' of the given way, so a 'wikidata=*'
tag is highly likely to be conserved. (If mappers simply replace one way
with another, obviously all bets are off, but that's already regarded as
impolite, particularly if they destroy existing tagging while doing so.)

If we abandon the idea that the back link must be to a single OSM object
and instead think of it as a link to a set of objects (ideally singleton, but
possibly zero, or more than one), to what extent does the problem go
away? The data link in both directions, and the tag is likely to be conserved
even when the underlying objects are restructured.

Is this at least the 90% solution? Will it buy us time and the opportunity
to grow into a better answer? What am I missing?

For what it's worth, I already maintain a few sets of [mostly imported]
objects in the database that bear tags whose values are
ID's in several foreign databases. "Any tag you like."
They are there precisely so that I can use them as forward links
and use Overpass queries as back links. I don't demand that they
be 100% stable, just that I have some likelihood of finding again an
object that I labeled once before. If mappers mess up a few of them,
it's no big deal, I don't expect crowdsourced data to follow any
external schema rigorously. Just as with anything else on the Web,
broken links happen sometimes. If the tags were deleted wholesale,
that would make me quite cross, particularly since we have no better
theory about how to deal (even approximately) with references between
our data and data housed in other repositories.

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