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DATETIME  July 2011

DATETIME July 2011

Subject:

Re: interval precision

From:

"Edward C. Zimmermann" <[log in to unmask]>

Reply-To:

Discussion of the Developing Date/Time Standards <[log in to unmask]>

Date:

Wed, 20 Jul 2011 11:35:57 +0200

Content-Type:

text/plain

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Parts/Attachments

text/plain (62 lines)

On Tue, 19 Jul 2011 14:31:26 -0400, Ray Denenberg, Library of Congress wrote
> We should avoid over-engineering. There is no need for a syntactic 
construct to indicate precision.
> 
> The precision of an interval is really not a concept that needs 
articulation.  If you have the interval:
> 
>     1960/9164-04
> 
> Then the start endpoint and end endpoint have their own precisions - year 
and month precision respectively.  These need not be the same, and the 
precision of the interval is simply undefined.
> 
> --Ray

An astute observation. It can't be defined.

[sidetrack: The interesting problem is that an abstract time interval is not 
really a set of discrete points of undividable precision but a fuzzy 
continuum with measurements always at some precision. If we judge time 
considering precision we have a clear well defined  element count for any 
interval and have a well defined set of points. The highest currently agreed 
upon ("interoperable") resolution of time is 1/9192631770 of a second (from 
the state transition of Caesium-133). If one second can have at most 
9,192,631,770 sub-points then 1 day can have at most 24*60*60*9,192,631,770 
or 794243384928000 elements-- by current computational standards a 
relatively small number (fits in 64-bit ints).]

Does it matter if its defined? For, at least my, typical questions I don't 
think so. For any time point (expressed in any precision) I can answer the 
question: "Is it within the given interval?"

Does "1960/1964-04" contain
- "1963"? Yes
- "1964"? Yes (since the precision of comparison can't ever be finer than 
the the precision of the least precise measure).
- "1964-04-12"? Yes
- "1964-05"? No

Other typical questions such as:
- Do the intervals overlap?
- Is one interval included in the other?
- Are the two intervals exclusive to one another (and, if so, their order)?
similarly follow....

With a higher level of (measurement) precision, of course, it might turn out 
that the date expressed as "1964" in the comparison was really "1964-05-
12T12:30" and this NOT in the interval but is it really the same comparison? 
The state of knowledge, afteral, is different. The same observation, of 
course, holds for intervals with the same precision for start and end when 
we increase precision. Increasing the precision--- just as increasing 
knowledge--- can sometimes lead to new and different conclusions....




--

Edward C. Zimmermann, NONMONOTONIC LAB
http://www.nonmonotonic.net
Umsatz-St-ID: DE130492967

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