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Wikifunctions:Type proposals/Julian calendar date

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Summary

A Julian calendar date identifies a specific day using the Julian calendar system introduced in 45BC, using the current numbering of years.

The Type is proleptic, i.e. it is also calculated backwards before its introduction. There is no year 0. Another type can be introduced that has a year 0. The Type is naïve with regards to UTC, i.e. it ignores it as it only resolves to the level of days. When we introduce Functions and Types with a higher resolution, we need to resolve possible discrepancies.

Uses

  • Why should this exist?

In order to be able to reference Julian dates and have functions that work with Julian dates.

  • What kinds of functions would be created using this?
    • How old was a person when they died?
    • How many days have passed between two days
    • What day of the week was a certain day
    • What is this date in another calendar? (requires the other calendar)
  • What standard concepts, if any, does this align with?

The Julian calendar date was historically widely used. It was introduced by Julius Cesar.

This is not the same as the time datatype in Wikidata, but it can be used in using it.

Structure

A Julian calendar date has the same structure as the Gregorian calendar date. Thus it has two keys:

  1. K1 of Type Gregorian year
  2. K2 of Type Roman day of the year

Example values

Value for October 27, 1014:

{
  "type": "Gregorian calendar date",
  "year": {
    "type": "Gregorian year",
    "era": "CE",
    "year": {
      "type": "Natural number",
      "value": "1014"
    }
  },
  "day of the year": {
    "type": "Day of the Roman year",
    "month": "October",
    "day": {
      "type": "Natural number",
      "value": "27"
    }
  }
}

{
  "Z1K1": "Znnn",
  "ZnnnK1": {
    "Z1K1": "Zppp",
    "ZpppK1": "Zqqq",
    "ZpppK2": {
      "Z1K1": "Z13518",
      "Z13518K1": "1014"
    }
  },
  "ZnnnK2": {
    "Z1K1": "Zmmm",
    "ZmmmK1": "Z16110",
    "ZmmmK2": {
      "Z1K1": "Z13518",
      "Z13518K1": "27"
    }
  }
}

Validator

The validator ensures that:

  • February 29 only appears in leap years
  • Further validation will be performed by the types used in the keys.

Identity

Two dates are the same if their day of the year and their year are the same.

Converting to code

We use the same as for Gregorian calendar dates.

Python

3 keys

1 BC is represented by 0, and 2 BC by -1, etc.

{
  'K1': 1014,
  'K2': 10,
  'K3': 27
}

JavaScript

3 keys

We will use the following object:

{
  K1: 1014n,
  K2: 9,
  K3: 27
}

Non-positive numbers for K1 represent the years BC, with 0 being 1 BC, -1 being 2 BC, etc.

Renderer

Renderers depend on the language. We will start with a general renderer outputting an ISO string as the default behaviour, i.e. “2014-10-27 CE”, but we will have a configuration that can be adjusted for a given language, e.g. "27 October 2014" or "le 27 octobre 2014 AD".

Parsers

Parsers depend on the language. We will start with a general parser that can take an ISO string as the default behaviour, but we will have a configuration that can be adjusted for a given language.

Alternatives

  • We could say we don't need this type, and use the Gregorian calendar date for both Julian and Gregorian calendar dates, and we need to remember which one is what out of context. That's potentially very confusing. It would also mean that the type is syntactically representing dates, but we don't really know what date it is. Also it would contradict what we said on Gregorian calendar date, where we said it means the Gregorian calendar date, and not just the syntactic representation of a date.
  • Should we use the Gregorian year, or do we need to introduce a Julian year to shadow the Gregorian year? Unlike with the date, I cannot see a disadvantage of using the same type for the year.

Discussion

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