Last year there was a little discussion about unique wikidata ids in the openstreetmap database: https://lists.openstreetmap.org/pipermail/tagging/2018-August/038249.html
It was more or less decided there was no problem with this. Nevertheless, I think we should consider having a hard rule of "*A Wikidata item cannot be connected to more than one OSM item*". Problems with not enforcing this rule: - the problem of a partially downloaded database, where one is never sure if a wikidata item is fully downloaded unless the whole database is downloaded. - we could get a flood of wikidata tags where one would, for example, tag every building in a town with the wikidata id of the town, because that building is a part of the town. Is that wrong tagging? Well, if the above rule is not in place, I'm not sure. - if a road segment has two road routes that are using it, then we should tag it as "wikidata=Q1234;Q5678". That means, if we want to find any wikidata id, we should be prepared to parse all wikidata tags and be prepared for semicolons. This slows down any wikidata searches - we can't enforce some rules like "tag leisure=stadium can only be connected to something that is, or is derived from Q483110 (Stadium) in Wikidata" because, if we tag all the parts of an entity, we can also tag a water fountain in the stadium, because that is a part of it. So I propose we enforce this rule, and we tag, for example, railways only on the route relation. If one wants to tag all route segments with a wikidata tag, I propose a general usage "*part:wikidata=**" which would be used when a single wikidata tag just isn't viable. Proposal wiki page here: https://wiki.openstreetmap.org/wiki/Proposed_features/part:wikidata Thanks for reading, Janko Mihelić
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