[Wikidata] calendar model screwup

Hi everyone, I have some bad news. We screwed up. I’m really sorry about this. I’d really appreciate everyone’s help with fixing it. TLDR: We have a bad mixup of calendar models for the dates in Wikidata and we need to fix them. ==== What happened? ==== Wikidata dates have a calendar model. This can be Julian or Gregorian and the plan is to support more in the future. There are two ways to interpret this calendar model: # the given date is in this calendar model # the given date is Gregorian and this calendar model says if the date should be displayed in Gregorian or Julian in the user interface Unfortunately both among the developers as well as bot operators there was confusion about which of those is to be used. This lead to inconsistencies in the backend/frontend code as well as different bot authors treating the calendar model differently. In addition the user interface had problematic defaults. We now have a number of dates with a potentially wrong calendar model. The biggest issue started when we moved code from the frontend to the backend in Mid 2014 in order to improve performance. Prior to the move, the user interface used to make the conversion from one model to the other. After the move, the conversion was not done anywhere anymore - but the calendar model was still displayed. We made one part better but in the process broke another part badly :( ==== What now? ==== * Going forward the date data value will be given in both the normalized proleptic Gregorian calendar as well as in the calendar model explicitly given (which currently supports, as said, proleptic Gregorian and proleptic Julian). * The user interface will again indicate which calendar model the date is given in. We will improve documentation around this to make sure there is no confusion from now on. * We made a flowchart to help decide what the correct calendar model for a date should be to help with the clean up. * We are improving the user interface to make it easier to understand what is going on and by default do the right thing. * We are providing a list of dates that need to be checked and potentially fixed. * How are we making sure it doesn’t happen again? * We are improving documentation around dates and will look for other potential ambiguous concepts we have. ==== How can we fix it? ==== We have created a list of all dates that potentially need checking. We can either provide this as a list on some wiki page or run a bot to add “instance of: date needing calendar model check“ or something similar as a qualifier to the respective dates. What do you prefer? The list probably contains dates we can batch-change or approve but we’d need your help with figuring out which those are. We also created a flowchart that should help with making the decision which calendar model to pick for a given date: https://commons.wikimedia.org/wiki/File:Wikidata_Calendar_Model_Decision_Tr… Thank you to everyone who helped us investigate and get to the bottom of the issue. Sorry again this has happened and is causing work. I feel miserable about this and if there is anything more we can do to help with the cleanup please do let me know. Let's please keep further discussion about this in one place on-wiki at https://www.wikidata.org/wiki/Wikidata:Project_chat#calendar_model_screwup Cheers Lydia -- Lydia Pintscher - http://about.me/lydia.pintscher Product Manager for Wikidata Wikimedia Deutschland e.V. Tempelhofer Ufer 23-24 10963 Berlin www.wikimedia.de Wikimedia Deutschland - Gesellschaft zur Förderung Freien Wissens e. V. Eingetragen im Vereinsregister des Amtsgerichts Berlin-Charlottenburg unter der Nummer 23855 Nz. Als gemeinnützig anerkannt durch das Finanzamt für Körperschaften I Berlin, Steuernummer 27/681/51985.