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

[robert_weir@us.ibm.com]

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

The _only_ thing we need to state in Part 2 is what happens when a date 
value is used in the context of a number.  In that case there is an 
implicit type conversion to a number, which is the number of whole days 
and the fraction of a day since an implementation-defined fixed point in 
time, called the epoch.

If we state only that much, then we encompass implementations, like Excel, 
where all user-dates are stored as numbers, as well as OpenOffice, where 
user entered dates are stored as ISO 8601 dates.  I think OpenFormula 
should be agnostic to that decision if it can.  That decision is really an 
application/user convention, not an OpenFormula issue.  It concerns what 
happens to a user-entered string and how it is stored.  Excel does it one 
way, OpenOffice another.  But that is outside of OpenFormula, which 
concerns how those stored formulas are calculated.

The semantics of calculations on dates is a bit murky.  Certainly adding a 
constant to a date, and subtracting two dates, these have obvious 
interpretations.  But spreadsheets also allow you to multiply two dates, 
etc.  Excel let's you calculation the value of SIN(DATE(2010,1,27)).  We 
can offer no interpretation to that other than a date is implicitly 
converted to a number, as stated above.  Saying anything more gets us into 
trouble.

The format of a number in a date format is the other side of the coin for 
the implicit conversion question.  But I think that is a Part 1 question 
for the presentation of table cell formats, but not a Part 2 question.

-Rob



From:
"Dennis E. Hamilton" <dennis.hamilton@acm.org>
To:
"'Patrick Durusau'" <patrick@durusau.net>, 
<office-formula@lists.oasis-open.org>
Date:
01/27/2010 02:28 PM
Subject:
RE: [office-formula] serial number? Don't we mean serial date?



I had been calling them ORDINAL DATES, but I realize they are really 
ordinal
DAYS.  You can call them SERIAL DAYS (but not dates).  I think that would 
be
fine.

They are not dates, they are just intervals of days (including fractions
thereof). 

I think these only become dates when taken with an origin date and the
calendar mapping that goes with that origin date.  Since different 
hostings
will have different defaults for this, and some will allow selection among 
a
variety of origin dates and calendar mappings (usually document-global and
not changeable except at serious risk). 

The value of a cell holding such an ordinal day may be displayed in a 
number
of ways (hh:mm is a format I use regularly, as is yyyy-mm-dd) as specified
for the presentation format of the cell.  The second (yyyy-mm-dd) requires
an understood origin date and calendar mapping.  In the spreadsheets I 
work
with regularly, the cell value is still a Number and it may even be
determined by a formula.

The value of a cell having specific type date (or date-time) will 
presumably
use any associated origin date and calendar mapping to make an ISO 8601 or
other standard date-time representation for its value, with that 
conversion
done as required by the OpenFormula hosting.  Likewise, values of cells of
type date, and constants of date form (not sure OpenFormula has those),
would be automatically convertible to serial days by reference to the
prevailing origin date and calendar mapping.

 - Dennis

-----Original Message-----
From: Patrick Durusau [mailto:patrick@durusau.net] 
Sent: Wednesday, January 27, 2010 10:50
To: office-formula@lists.oasis-open.org
Subject: [office-formula] serial number? Don't we mean serial date?

Greetings!

I am doing triage on the data types and keep running into date being 
referred to as a serial number?

Surely we mean serial date?

But it happens so often that I wanted to ask before changing it.

Hope everyone is having a great day!

Patrick

-- 
Patrick Durusau
patrick@durusau.net
Chair, V1 - US TAG to JTC 1/SC 34
Convener, JTC 1/SC 34/WG 3 (Topic Maps)
Editor, OpenDocument Format TC (OASIS), Project Editor ISO/IEC 26300
Co-Editor, ISO/IEC 13250-1, 13250-5 (Topic Maps)


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