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Re: [ontolog-forum] Time representation

To: "[ontolog-forum] " <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Pat Hayes <phayes@xxxxxxx>
Date: Mon, 21 Jan 2008 16:00:31 -0600
Message-id: <p06230901c3bac2d1886a@[]>
At 12:48 PM -0500 1/21/08, John F. Sowa wrote:

The position I most strongly advocate is not a specific ontology,
but a framework of conventions for organizing a multiplicity
of special cases (not necessarily consistent with one another),
making the implicit relationships explicit, and providing tools
and guidelines for mixing and matching.

If you look at the original OWL-Time ontology, before it became OWLized, that is exactly what Jerry H. did. There were actual propositions which one could assert, like (continuousTime) and (branchingTime) , or their negations, and the axioms were written with internal conditionals which selected the appropriate content for each case. The result is however rather awkward to read, to put it mildly.

In practice, I think a single, fairly simple, ontology is best for handling time. It should be agnostic on whether time is ultimately continuous or dense (because either choice gives far more complexity than one ever wants in practice) , ignore branching and circularity, have real but severely limited ability to speak of intermittent intervals like 'every tuesday afternoon', and have a very rich system of times and dates, savvy enough to keep track or real calendars (knows about timezones, summer times, notions of appropriate timescales, etc..

The lattice of theories
is an example.  Robert Kent's IFF is a much more ambitious example.

I would recommend a fairly simple framework for starters, since
there's a danger of freezing half-baked ideas before they're fully
baked.  (RDF, for example, was hardly out of the oven before
Tim Bray tried, unsuccessfully, to pull it back in.)

 > Do you have any granularity axioms?  That is one of the hardest
 > ontological problems, in my experience.

There are so many hard problems, it's hard to say which are harder.

Harder = having been noted and tackled more times without success.
But the idea of taking the least significant digit as the criterion
for implicit granularity is fairly common for experimental data
(unless some explicit margin of error is stated).

Thats fine if you have digits to work with, but you usually don't.

Re PTim: I realize that calling an interval a point is problematical.
But in anything that has to do with the physical world, there is no
way to specify a true point.

But we can talk about them without specifying them numerically. They are limit constructs so inherently require infinite amounts of information to specify quantitatively. But I think we do specify points by description, eg "when the light came on". Certainly some reasoning is a lot easier if we can treat time points as being real points, eg it means that ordering needs only 3 cases (< = >) instead of 13.

  Perhaps a better term would be "grain
in time", abbreviated "Grit".

:-)  In the old survey I used 'moment' for a chunk of time with no smaller subchunks, and then the issue is whether moments are points. I think you would say that moments only exist at a given granularity, right?


PS re HTML email formats:  Your note of 11:18 was in a readable font
for Thunderbird, but your note of 11:37 appeared in a tiny, tiny font.
I had to increase the font size by two steps to make it the same as
the previous note.  But then the fonts for all other notes were too
big, and I had to decrease the default by two steps.

Yes, sorry, that was a (temporary) artifact of replying to a Thunderbird-read email in Eudora. Won't happen again.

At least each of your notes was entirely in one font size.  I've
received some email in which each paragraph was in a progressively
smaller font.

Ha. I get some where each reply comes back in a progressively larger size, like the guy is shouting louder and louder. Hmm, maybe that was deliberate.....


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