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Support dates with unknown year but known month/day
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Description

Sometimes people will give their birthday but not their year of birth. As far as I can tell, it's not possible to enter these (if it is, I haven't figured out how).

For example, the date of birth of https://www.wikidata.org/wiki/Q11194654 is the 27th of August according to http://cleanero.com/profile.html but no year is given. Most of the pages in https://ja.wikipedia.org/wiki/Category:%E7%94%9F%E5%B9%B4%E9%9D%9E%E5%85%AC%E8%A1%A8 ("birth year unknown") also only have the month and day.

It seems that ISO 8601 supports these by using a hyphen to represent the unknown part, e.g. --02-03 for the 3rd of February in an unknown year.

Note that this is similar to, but distinct from, recurring dates.

Event Timeline

Nikki created this task.Jul 4 2015, 1:18 AM
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daniel triaged this task as Low priority.Sep 10 2015, 3:40 PM
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What I forgot to mention here is that it can appear like this is already supported, because you can enter "August 24" (for the example in the description), but that actually means the year 24 AD, not the 24th day of the month. The ticket for making that more obvious is T104750.

Jc3s5h added a subscriber: Jc3s5h.Mar 9 2016, 2:34 PM

Following a request for jawiki, there is now https://www.wikidata.org/wiki/Property:P3150 (birthday) with item-datatype.

While machine readability of these items could be improved, in terms of maintenance, I think it can be an advantage if this isn't combined in P569 (date of birth). Personally, I wouldn't include such dates in time-datatype properties.

daniel closed this task as Declined.Sep 13 2016, 5:34 PM

Assuming this requests support for partial dates in Time values, I'm declining this for technical and semantic reasons. A Time data value represents a specific point in time (with some level of uncertainty). It doesn't represent a partial date or recurring date. Mixing partial or recurring dates with points in time would be confusing (especially for machines), they should not use the same data type nor the same properties.

If you think we need support for this kind of incomplete dates (how is this different from recurring dates?), please request a data type to be added for this. A new data type would also mean separate properties.

On that note, using P3150 for birthdays as @Esc3300 mentions, and referring to the appropriate item representing the relevant day-of-the-year, seems like a good solution to me. Is that not sufficient?