My last blog post triggered a couple of responses on Twitter. It seems I touched a problem that will not be solved that easily.
Save dates as Julian on your Wikibase (manually or, with the /J switch, in your QuickStatements mass input) and your Wikibase will be able to handle these dates correctly in any mixed bag of Julian and Gregorian dates. It is nice that the Query Service is able to produce straight timelines out of any such mixed bag, but immensely problematic that you will be quite unable to get the original Julian dates back in regular Query Service downloads. Blazegraph, the tool that is working behind the Query Service, does its job on normalisations of dates, and these are, of course, performed in the superior Gregorian calendar. Wikibase Query Services are hence on their way to produce loads of unprecedented arithmetical Gregorian dates in environments that have been solely Julian so far. We will first be puzzled by dates that strangely differ from those we fed into these machines — we will have to understand that they have silently added days on them to reach their Gregorian equivalents. Handle these artefacts as correct Gregorian dates, though they are without evidence in the historical records — do not feed them as Julian into any Wikibase because that will immediately expose them to the next round of Julian to Gregorian conversions wherever a Query Service will spot them.
SPARQL queries can actually produce the complexity of the Wikibase they are accessing, but that requires quite some scripting skills. Tagishsimon gave the following script that helped him to get well informed dates from Wikidata in this Twitter response:
Per Bruno, SPARQL/WDQS will give you all of the data required to convert a Gregorian date back to a Julian date, it's just a bit of a clart. pic.twitter.com/S3gBpO93cp
— Tagishsimon (@Tagishsimon) March 20, 2024
Bruno Belhoste applied this script in the following FactGrid query, which will be extremely useful in all future searches on our database. The table gives you the birthdays of members of the French Academy — a typical “mixed bag” of dates that shows all imaginable challenges of different calendars and the various precision statements:
Change the parameters and you will get the dates you are interested in with all the information you will need to process a mixed bag of historical dates from the Wikibase of your choice.
A make shift solution: The “Julian Calendar Stabiliser”
We agreed that we have to stabilise Julian dates on FactGrid under these conditions. All Julian dates will be translated to Gregorian sooner or later on our Query Service. Users must, hence, remain able to get the original Julian information side by side with their (secretly Gregorianised) searches. The simple solution is a string repetition of the Julian statement you want to make. The Query Service does not touch strings, chains of characters and numbers; it will give you the original Julian statement which you can use in other contexts as the very dates you saw in your documents:
This is not the ideal solution. One would rather like to have a calendar sensitive Query Service that produces dates as stated on your Wikibase; but it is at least a pragmatic stabilisation to keep Julian dates intact in the waves of transformations and deformations which we are likely to witness in the new world of data processing.