Subject: RE: Are date ranges half-open?

From: [email-masked]
Date: Wed, 28 Mar 2001 15:15:50 -0600

> I've always though of the span of time of an event as a half-open
> interval. That is, the event includes the start time but does 
> not include
> the end time -- it ends some infintesimal moment before.
> 
> But Frank suggested in an example in a previous thread that 
> an event of a
> duration of one day is represented as:
> 
> DTSTART;VALUE=DATE:20010328
> DTEND;VALUE=DATE:20010328      
> 

If the end date is the same as the start date, then it still starts on the
28th. 

So, you are saying that this is the same as an event with just the DTSTART?
Right? RFC2445 states in the definition of DTSTART that this condition is
the same as an event that doesn't take up any time. So, I would say that my
example specifies such a condition.

Your comment about viewing DTEND as not being inclusive seems correct. So to
take up a day, the DTEND value should have been the 29th. But I still think
that this is the same as a DURATION value of P1D ;-)

-- Frank

---

From: [email-masked]
Date: Wed, 28 Mar 2001 15:44:10 -0600

> This should be explicitly stated, but I would think
> that Time spans should be half-open, and that this should
> be stated in the spec. Otherwise, a one hour event starting
> at T150000 would end at T155959, which looks to me like an
> interoperability nightmare.
> 
> It would seem logical that date spans should be consistent
> with time spans, but either way it should be explicitly
> stated.
> 

I may need a cafeine break, but I was thinking that I was applying the
calendar and time scales for duration in a consistent way. You add the
scalar of the duration to the start. 

The issue was that some folks were converting the calendar scale into a time
scale. In such mixed scale cases (i.e., DTSTART in date-time...effectively a
time scale and the end/DURATION in calendar scale), I would have used the
date-time to determine the calendar scale and then apply the duration to
that.

But enough...

-- Frank