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Subject: Re: [office] Excel 2007 != Ecma spec YEARFRAC. Not even slightly. What should we do?


Rob,

 From below:

> The problem we have is there are more defined conventions in existence 
> than the 5 bases in Excel.  There appear to be at least 10 different 
> defined conventions in use. You can see them enumerated here:
>
> http://www.eclipsesoftware.biz/DayCountConventions.html 
Well, since you found them perhaps you should invite them to join the TC 
and the formula SC. They appear to have a lot of resource information 
and one suspects expertise in the area.

Hope you are having a great day!

Patrick


robert_weir@us.ibm.com wrote:
>
> Patrick Durusau <patrick@durusau.net> wrote on 04/17/2008 10:34:00 AM:
>
> > Well, except that the definitions by the "authorities" are at least as
> > vague and/or ambiguous as those of #2. If such "authorities" did have
> > complete definitions it would be the "logical and defensible" approach.
> > Unfortunately, I don't think those have ever been defined.
>
> I think you are being needlessly pessimistic.  Just because Microsoft 
> hasn't managed to define these conventions doesn't necessarily mean 
> that others have not succeeded.  
>
> If you look around, you will find fuller, authoritative definitions 
> for some of these conventions.  
>
> For example:  http://www.isda.org/c_and_a/pdf/ICMA-Rule-251.pdf
>
> Real money is on the line.  Being one day off on a date calculation 
> may be only 0.3% in a year, but when dealing with a 100 million dollar 
> transaction that is real money.  
>
> The problem we have is there are more defined conventions in existence 
> than the 5 bases in Excel.  There appear to be at least 10 different 
> defined conventions in use. You can see them enumerated here:
>
> http://www.eclipsesoftware.biz/DayCountConventions.html
>
> There is no easy way to tell whether what Excel does is:
>
> 1) Exactly the same as one of these conventions
> 2) Based on an earlier version of the these conventions
> 3) A buggy implementation of one of these conventions
> 4) A 100% correct and current implementation of some other conventions 
> that are close but not identical to any of these conventions.
>
> So putting together a set of well-defined date counting conventions 
> based on external authorities -- this is easy.  But the task of doing 
> that and being compatible with Excel -- this is not so easy.
>
> Maybe the solution is to have more than 5 bases?  We let 0-4 be the 
> "Excel-compatible" options that match, as much as we can ascertain, 
> what Excel 2007 does.  Then we have additional options 5, 6, 7, etc., 
> that match current external financial authorities exactly.  
>
>
> -Rob
>
>

-- 
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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