On Thu, Nov 17, 2011 at 3:40 PM, CRPence <CRPbottle@xxxxxxxxx> wrote:
On 15-Nov-2011 22:13 , John Yeung wrote:
IBM's "Julian dates" have as much to do with *actual* Julian
dates as Julian Lennon.
Most references to a "Julian date" [for IBM i anyhow]
likely apply only to a presentation-format and\or input-
format for Gregorian date values.
This is my point exactly. There is no reason for that *format* to be
called Julian, because there is no relationship between that format
and any variation on the Julian date system. Even the astronomical
Julian date system (a) uses the Julian calendar, and (b) is a number
of days from a single fixed point in all of time, not from the
beginning of EACH year.
Did Julius Caesar express dates as a year and a number of days from
the beginning of that year? No. He used 12 months, and days within
the month, just like we do today. So where does "Julian format" come
from?
The terminology was even worse at my previous job. There, "Julian
date" specifically meant YYDDD, "extended Julian date" meant YYYYDDD,
"Gregorian date" meant YYYYMMDD, and "calendar date" meant MMDDYY.
the database [AFaIK still] only supports the Gregorian
calendar [though, with the skipped\missing days
accounted\included] for date calculations.
First of all, there would be no useful reason to support anything
other than the Gregorian calendar. It's what the entire world uses,
at least when interacting internationally. (There are religious,
cultural, and local calendar systems that may be used internally by
those religions, cultures, or localities.)
Second, I'm not completely sure what you mean by skipped/missing days.
Are you referring to the point at which England switched from the
Julian calendar to the Gregorian, and thus had to enact a one-time
correction? Unless you are a historian and your data actually uses
dates from that time (and keep in mind that different areas of the
world switched to Gregorian at different times; Russia was still using
the Julian calendar until 1918!), it really only makes sense to do all
calculations as if the Gregorian calendar had always been in effect.
(And this is what the IBM-supplied functions do.)
I will say this: I have seen a lot of home-grown date code that
calculates as if the Julian calendar were in effect! (Specifically,
any code that assumes *every* 4th year is a leap year is effectively
using the Julian calendar, and not the Gregorian calendar.)
John Y.
midrange.com
