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DATETIME  August 2016

DATETIME August 2016

Subject:

International Calendar vs. EDTF

From:

Christoph Päper <[log in to unmask]>

Reply-To:

Discussion of the Developing Date/Time Standards <[log in to unmask]>

Date:

Thu, 11 Aug 2016 14:59:29 +0200

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Hi!

My name is Christoph Päper. I’m a regular contributor to [log in to unmask], maintain most of calendars.wikia.com, regularly contribute to calendar and other topics on Wikipedia (as user Crissov on both sites) and are overall a standardization geek (mostly active at W3C). Although I’m fascinated by calendar reform proposals, I very much realize – unlike some people at Calndr-L – that they’re unrealistic for the most part and standards should foremost document existing (good) practice. That being said, date and time notation is an area that can propagate new conventions, cf. the week year established by ISO 8601 and its predecessors (and ignored by EDTF).

Yesterday, I learned that ISO 8601 is currently under review and I’ve been pointed to EDTF, which I sadly didn’t know about before. Several years ago I started to collect and develop ideas on how to improve and extend ISO 8601. The (incomplete) result of that is documented as the “International Calendar” (IC) at <http://calendars.wikia.com/wiki/International_Calendar>. 

Some of its features are also specified in the EDTF proposal and hence ISO/WD 8601-2 (which I found in the list archive, dating from February), e.g. ‘X’, and I have to admit that the notation of uncertain or approximate dates is much more elaborate in EDTF than in my IC. It’s very useful for bibliography, genealogy, archaeology and other historic sciences, but could also be used for fuzzy database requests.

I do believe, however, that IC handles quarters better than EDTF, although I confess that it didn’t occur to me before to reuse MM with values well above 12. IC adopts and generalizes two important rules from ISO, which I’ll paraphrase slightly different here:

1. “Thursday rule”: A calendaric entity belongs to a longer-lasting entity that the majority of its own subparts belong to:
  - A week belongs to the month, quarter or year that 4–7 of its days belong to. 
    (It’s only explicitly used for year by ISO currently.)
  - A month belongs to the quarter or year that 16 or more of its days belong to. 
    If it has 15 or fewer days in either quarter or year, it belongs to the one 3 of its weeks belong to.
  - A quarter belongs to the year that 46 or more of its days belong to. 
    If that’s ambiguous, it belongs to the year 7 of its weeks or 2 of its months belong to.

2. “Letter marker”: Non-fractional items other than year, month, day, hour, minute and second should have a single-letter prefix, e.g.:
  - ‘W’ for weeks (This is the only prefix currently used by ISO.)
  - ‘Q’ for quarters
  - ‘S’ for seasons
  - ‘M’ for non-Roman months
  - ‘L’ for lunations

A similar rule to #2 is that the number of digits, kind of separators and prefixes together determine which format a date-time string uses, never the values of its digits. EDTF’s -2X season notation breaks that rule, because CCYY-MM = CCYY-SS (with M₁ ∈ {0, 1} ∌ S₁ = 2). I’d agree, though, that encoding 12 different values with 2 fixed digits is a waste of space (leaving 88 combinations unused).

An exception to #2 are IC’s “triads” (or trimesters) which are 3 consecutive months each, starting with January, because they are written as CCYY-Q (no marker, but mandatory hyphen). Week-based quarters, or “quarts”, use ‘Q’ and astronomic seasons use ‘S’. Due to #1, Northern winter (‘-24’ in EDTF) is ‘S1’, i.e. the first season of the year. Since month, week and day are all ordinal (1-based), it would be strange (though possible) to make ‘CCY0-S4’ equal ‘CCY1-S0’ (cf. 0-based hours). This problem also applies to common academic terms in the Northern hemisphere.

Quarter notation involving ‘Q’ is already popular, e.g. “2016Q3”, but in commercial contexts, this often relates to the fiscal or tax year, which may start any time or at least any month or week in many jurisdictions, so differs from company to company.

IC doesn’t need a ‘Y’ prefix like EDTF, because plus ‘+’ is mandatory for years after 9999 and extended format (i.e. involving field separators ‘-’ and ‘:’) is required with signed years (and becomes the default format overall). I really hope ISO 8601 will adopt that convention. The “paving cow paths” approach, on the other hand, would be to follow common patterns found in archaeology, astronomy etc., which use acronyms or symbols for thousands, millions and billions of _years ago_, e.g. ‘kya’, ‘Mya’, ‘BYA’ (date) or ‘Ga’ (age).

I strongly believe ISO 8601 should prescribe the proleptic Gregorian calendar and call it the “International Standard Calendar”. The Julian calendar had been the dominant calendar of Europe/Christianity for ca. 16 centuries before the Gregorian reforms, but any date before that originally used a different calendar anyway. Maybe, though, it’s enough to support months and weeks only for the Holocene/Anthropocene, i.e. with 4-digit years.

Just in case, let me assure you that I don’t believe all of IC should be part of ISO 8601, for some of it specifically targets the alternate calendar community (e.g. full-week months, days outside the week cycle).

Cheers

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