[cabfpub] Durations

Peter Bowen pzb at amzn.com
Sun Feb 5 14:09:19 MST 2017


Kirk,

> can't machines be programmed to notice that April 18, 2017 is 13 months after March 18, 2016?

Of course.  Computers can be programmed to solve very hard problems and are do so every day.  That being said, this is actually much harder than it might seem at first glance because the Gregorian calendar is non-uniform.

Consider a fairly simple case: Starting from March 31, 2017, when is the end of 13 months?  Is it April 30, 2018 or May 1, 2018?

And a slightly more complex case: Starting from Feb 28, 2015, when is the end of 13 months?

Once these are resolved, we can get to rules on calculating months, but these are highly subjective.  I don’t really want to have a whole appendix on calculating dates if I can avoid it.

Thanks,
Peter

 

> On Feb 5, 2017, at 12:32 PM, Kirk Hall via Public <public at cabforum.org> wrote:
> 
> Gerv - can't machines be programmed to notice that April 18, 2017 is 13 months after March 18, 2016?  It seems easy to do that, and much easier for humans to evaluate than 398 days.
> 
> -----Original Message-----
> From: Public [mailto:public-bounces at cabforum.org] On Behalf Of Gervase Markham via Public
> Sent: Sunday, February 5, 2017 1:26 AM
> To: CA/Browser Forum Public Discussion List <public at cabforum.org>
> Cc: Gervase Markham <gerv at mozilla.org>
> Subject: Re: [cabfpub] Durations
> 
> On 04/02/17 22:16, Kirk Hall via Public wrote:
>> Peter - don't you think "13 months" already encompasses all cases like 
>> what you show below (start date and end date 13 months apart based on 
>> the dates themselves, even if that means the number of days varies a 
>> little), and will encompass all situations, like when the 13th month 
>> has 28, 29, 30 or 31 days?
> 
> We want a definition which is both easy to explain to humans, and easy for computers to verify. Subtracting two dates to get a single number of days between is an easy thing for a computer to do (with the appropriate library), and comparing that to a defined number is also simple.
> 
> So a definition like "398 days (just over 13 months)" fits both criteria IMO.
> 
> Gerv
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