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Re: [ontolog-forum] Time representation

To: "[ontolog-forum] " <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Pat Hayes <phayes@xxxxxxx>
Date: Tue, 22 Jan 2008 11:19:29 -0600
Message-id: <p0623090cc3bbd3e98a7e@[10.100.0.22]>
At 4:47 PM +0000 1/22/08, Ian Bailey wrote:
>Hi Pat,
>
>In a 4D Ontology, what you refer to as a point in time is actually an extent
>with one dimension (time) tending towards zero and the other three tending
>towards infinity.    (01)

Hi. I'm familiar with the 4-d approach, and like 
it: but the 4-d vs. continuant debate is a tarpit 
of endless debate which we can avoid while 
sticking closely to the topic of time.    (02)

When discussing 4-d, time is indeed a dimension, 
so the intervals/points discussion is about the 
structure of that particular coordinate.    (03)

>More usually, one is interested in a "point in time" over
>a finite 3D extent though (ignoring relativistic considerations, which in
>most earth-bound situations we can    (04)

Yes, lets please ignore relativity. Never mind 
earth-bound: the Voyager probe got all the way to 
the Kuiper belt using Newtonian physics.    (05)

>). We can talk about 4:00 UST all over the
>world. That is not a point, it's an extent in four dimensions.    (06)

4:00 all over the world is a 3-d extent in 4 
dimensions, forming the temporal boundary of a 
4-d entity which we might call 3:00-to-4:00 all 
over the world. However, 4pm is indeed a point on 
the time axis, the projection of 4:00 all over 
the world onto that axis.    (07)

>I'm sure Chris Partridge or Matthew West can explain this more precisely
>than me, so apologies if my terminology is not quite correct.
>
>>From a purely pragmatic point of view (I'm what Chris describes as a
>"hairy-arsed engineer"), 4D works and works very well - we've been working
>with for years in ISO15926, and we chose the same approach for the IDEAS
>Ontology (www.ideasgroup.org) 'cos it works. I've seen far too many bodged
>and inconsistent attempts to manage time in data models and ontologies over
>the years. The 4D approach gives you a pattern for representing change over
>time that works in all cases and works consistently.    (08)

I agree wholeheartedly. One of the worst 
decisions in recent ontology engineering has been 
the rejection of the 4-d approach in the medical 
ontology standards such as BOF and DOLCE. Putting 
these into a 4-d framework eliminates the useless 
and confusing need to duplicate content in two 
'styles', once for continuants (things) and the 
other for occurrents (events).    (09)

Pat    (010)

>
>Cheers
>--
>Ian Bailey
>www.modelfutures.com
>T: +44 207 193 4605
>M: +44 7768 892362
>Skype
>
>Model Futures Limited is a company registered in England and Wales with
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>
>But those start and end times ARE points. Really,
>you can't get away from it: if you have
>intervals, you have the points at their ends.
>They might not be points in the mathematical real
>line, but they are points in the following senses:
>
>1. they are indivisible (unless you change your interval topology)
>2. they are the places where intervals meet one another
>3. they are uniquely determined by your intervals
>4. they determine the time ordering on the intervals
>
>And this is independent of whether or not you have continuous or dense time.
>
>Pat
>
>
>>All this for me is independent of whether time is ultimately granular
>>or continuous. Ultimately this only means at what point we can not longer
>>tell whether one event happened before another.
>>
>>
>>Regards
>>
>>Matthew West
>>Reference Data Architecture and Standards Manager
>>Shell International Petroleum Company Limited
>>Registered in England and Wales
>>Registered number: 621148
>>Registered office: Shell Centre, London SE1 7NA, United Kingdom
>>
>>Tel: +44 20 7934 4490 Mobile: +44 7796 336538
>>Email: matthew.west@xxxxxxxxx
>>http://www.shell.com
>>http://www.matthew-west.org.uk/
>>
>>
>>>   -----Original Message-----
>>>   From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
>>>   [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx]On Behalf Of
>>>   John F. Sowa
>>>   Sent: 21 January 2008 17:48
>>>   To: [ontolog-forum]
>>>   Subject: Re: [ontolog-forum] Time representation
>  >>
>>>
>>>   Pat,
>>>
>>>   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.  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.
>>>   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).
>>>
>>>   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.  Perhaps a better term would be "grain
>>>   in time", abbreviated "Grit".
>>>
>>>   John
>>>
>>>   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.
>>>
>>>   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.  That's why I hate HTML email.
>>>
>>> 
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>
>
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phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes    (012)


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