Coming back to Magnus's suggestion ... I think the existing property "retrieved" (P813) could be used for this "last verified on" property, that is, for setting the time a which some external reference was last compared to a claim in Wikidata.
Magnus also pointed out that many external IDs are "self-verifying" in that they are their own reference. The situation is somewhat similar for homepages. Should we adopt the practice of giving a single retrieved value (without any further information) as the reference for such cases?
Adding P813 dates more widely would also open up new ways of maintaining data, since one would have a way to filter statements by how long ago they had last been checked.
Best wishes,
Markus
On 03.06.2015 15:56, Markus Krötzsch wrote:
On 03.06.2015 13:57, Magnus Manske wrote:
Maybe there is a case to separate import and verification here?
There are many statements in Wikidata nowadays, but they get really "trustworthy" through references (other than "imported from Wikipedia"). But for external IDs, references are superfluous; they are their own reference, by definition. So how about marking IDs with a "verified" (or "last verified on") qualifier? Much of such work could be done by bots; we could then filter the problematic ones out for manual verification.
As we have no control over external lists, this would have to be re-checked ever so often; but, again bots to the rescue.
Yes, I fully support this proposal.
What do you think about making "last verified on" not a qualifier but (part of) the reference information? The reference could state where the bot has looked up the ID and give a time. This would be somewhat similar to what is now used in Freebase Ids, e.g., in https://www.wikidata.org/wiki/Q42.
In general, it might be useful to have such a "last verified on" property that can be added to arbitrary references. There are many other uses for this. One common case would be that a user has changed the value without even being aware of the reference -- then one would be able to detect this automatically by comparing the last modification time with the "last verified on" date.
Putting the "last verified on" into the references also makes it possible to have different dates for different references there.
Regards,
Markus