RE: [office-formula] serial number? Don't we mean serial date?

["Dennis E. Hamilton" <dennis.hamilton@acm.org>]

Rob, I mainly agree that there is no "type," Serial Day, but there are an
incredible number of places where the current OpenFormula functions produce
and accept Number values that are interpreted as serial-day values as part
of the definition of those functions.

I agree we should abstract this.  But I don't think we can avoid talking
about the serial-day interpretation of Number type values.  There are also
some quality matters to consider, such as what the minimal fraction of a day
is that must be reliably represented and what the corresponding limitation
on the span of serial days becomes for adequately-approximatable date-time
and for exactly represented dates, respectively.

 - Dennis

PS: I think epoch is an unfortunate choice, because it confuses the
origin-date assigned to serial day 0 or serial day 1 in a mapping with what
year 0 or year 1 of a given calendar system represents in terms of
historical events.  These strike me as independent.  (Geological epochs we
don't confuse with, one would hope.)

THE USUAL ADDITIONAL THOUGHTS

Many OpenFormula functions depend implicitly on the global origin-date/epoch
value and the calendar mapping that goes with that origin date.  This is
true for anything involving a start-date and end-date parameter, especially
YEARFRAC and anything that has time-period basis adjustments that depend on
the actual calendar periods involved.  We can't define these functions
without acknowledging the existence of a mapping known to the implementation
of the functions and talking about the dates those mappings correspond to.
The DATEDIF function is a particularly interesting case of this
interdependence.

The other wrinkle is if there are mappings to and from text strings as part
of OpenFormula itself.  If any of those mappings involve date formats (not
numbers), the issue shows up there too both for literals and string values
received from references (although we could have an implementation finesse
that case, just as for Logical/Number).  [I don't recall seeing anything
that would make or take a string holding a calendar date, but I am hedging
my bet here.]



-----Original Message-----
From: robert_weir@us.ibm.com [mailto:robert_weir@us.ibm.com] 
http://lists.oasis-open.org/archives/office-formula/201001/msg00098.html
Sent: Wednesday, January 27, 2010 11:46
To: office-formula@lists.oasis-open.org
Subject: RE: [office-formula] serial number? Don't we mean serial date?

This is really very simple.  We don't need to refer to serial dates at 
all.  There are dates and there are numbers. 

[ ... ]