Subject: Are date ranges half-open?

From: Eric Busboom <[email-masked]>
Date: Wed, 28 Mar 2001 12:44:46 -0800 (PST)

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 you think of date spans as half open, then this event consumes no time
-- it ends just before 28 March, before the event starts. 

Since this is inconsistent with time spans, should we define date spans to
be on half-open intervals like time-spans? I don't think the Spec
specifies it one way or the other. 

In fact, I don't think the spec has anything to say about time
spans either. Perhaps we should include some text the defines the end date
or time to not be part of the interval?

eric.

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From: Alan Davies <[email-masked]>
Date: Wed, 28 Mar 2001 16:01:32 -0500

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.

--Alan

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From: John Stracke <[email-masked]>
Date: Wed, 28 Mar 2001 16:31:16 -0500

Eric Busboom wrote:

> interval.

Same here.

> be on half-open intervals like time-spans?

I would say yes.

> spans either.

In the case of time spans, there's a tendency to shrug off the question,
because it's only a question of whether a single second falls into the
range.  For date spans, though, this approach definitely breaks down.  (Even
for time spans, I think it's risky; in the CPL case, for example, if you're
in that single second, it's an important question.)

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