EDIT: I initially used the term “maintenance”/“maintaining” for different ideas. Placekey are the “maintainers” (i.e. gatekeepers) of the Placekey IDs in the sense that they to decide which IDs exist and what object(s) those IDs they identify. The other kind of maintenance is keeping the IDs on OSM updated. So I updated the rest of the post to use “gatekeeping” and “maintaining”, respectively, for these two ideas as I initially meant them.
From a quick read of their homepage, I think they serve as the gatekeepers of IDs. Is that something acceptable for OSM? I’m not sure… See for example this excerpt (emphasis mine):
If a specific place has a location name (like “Central Park”) and is already included in the Placekey reference datasets
In more practical terms, how would this be used? This question applies also to @fititnt’s previous post.
Other than that, Placekey doesn’t seem to be a suitable ID system because someone has to be the gatekeeper (the OSM infrastructure), and it’s not stable (see next).
If I understood correctly, it can be used for locations as well as amenities/businesses/etc.
So let’s assume there’s a feature X at place Y, assume that X is the set of tags that represent the type of feature (e.g. restaurant, bakery, clothes shop, …), its name, and other things that may distinguish it from other features around it, assume that Y is the set of
addr:* tags (complete and corect) and/or the geospatial coordinates.
From X & Y we can get a placekey ID (say,
X@Y). Do we add a
placekey=X@Y? If yes, who’s gonna maintain it? How can we enforce it being added? How can we prevent it being removed?
What happens if said restaurant changes places? Now, instead of at Y, it’s at Z. The placekey changes because it has the place encoded in it:
X@Z is the new ID. If we’re supposed to add
placekey, we have to change it to
placekey=X@Z, right? Hence it’s not stable.
And what happens if, for example, the name changes (by mistake, the name really changed, or whatever else)? W is now the set of tags representing the type of feature. The Placekey ID is now
W@Z. Not stable, again.
In short: whatever stable unique ID system we want, whether it already exists or not, it can’t depend on geospatial location; it can’t depend on small differences in tagging; at the same time, it mustn’t depend totally on the features not changing at all; and ideally it doesn’t need gatekeeping.