On Thu, February 3, 2011 4:37, Pat Hayes said:
> Ian, here's a non-philosophical way to characterize it. Start with an
> atomic sentence of the form R(a, b), with no time involved, and suppose
> that a and b here are ordinary uncontroversial physical objects, say.
> Intuitively, they are 3D things. Now add time, t. Where do we put the time
> parameter? Several answers can be given. (01)
Pat, i like this description of 3D, 3D+1 and 4D. (02)
> 1. Attach it to the sentence, meaning that the sentence R(a,b) is true at
> the time t. This gives you a hybrid or context logic where the times are
> possible temporal worlds/indices or contexts, to which truth is
> relativized. But the sentences being so relativized do not themselves make
> any reference to time. Call this 3D.
>
> 2. Attach it to the relation as an extra argument, and call the relation a
> 'fluent': R(a, b, t) This gives you the classical AI/KR approach which
> used to be called the situation calculus, where one quantifies over times
> in the KR language itself, but the object terms are still thought of as
> denoting 3D rather than 4D entities. Call this 3D+1.
>
> 3. Attach it to the object terms (using a suitable function, written here
> as an infix @): R(a@t, b@t) This requires us to make sense of this @
> operation, and it seems natural to say that it means the t-slice of the
> thing named, which now has to be re-thought as a 4D entity. So the a, b
> things have morphed form being 3D (but lasting through time) to being
> genuinely 4D, and having temporal slices or parts. Call this 4D.
>
> For some folk this last step is apparently mind-boggling, although to me
> it is puzzling how one can think of something being 3D and also extended
> in time and have it *not* be 4D. (03)
One problem that people have with considering this 4D is that the 4th
dimension is different. A physical object may be repositioned in any of
the three normal dimensions, but it can not be rotated in the fourth
dimension. Of course, nothing can happen to such a 4D object (unless a
fifth dimension is invoked), whereas an object with four spatial di-
mensions could conceptually be rotated so that different parts of it
intersect the conventional three dimensional space. (04)
> For yet other people (think OBO), there
> are apparently two kinds of thing in the world, one kind (continuants)
> which must be described using the 3D+1 style , the other (occurrents)
> which should be described using the 4D style. God alone knows why anyone
> would believe that there are two ways to exist in time, but there's nowt
> as queer as folk, as someone's grandmother used to say. (05)
Don't you consider the distinction between physical objects and events/
occurrences to be ontologically meaningful? Why should it be curious
for some people to think that elements of the two different categories
exist in different fashions? (06)
It is also useful to note that in a 4D model, aspatial temporal objects
(accounts, laws, theories, ...) are one-dimensional objects. (07)
> What I like about this way of contrasting the options is that it makes it
> be simply a matter of syntax - where in the sentence to attach the
> temporal parameter - and not one of metaphysics. (08)
So do i. (09)
-- doug f (010)
> Syntax is way easier than
> metaphysics. It also means that one can see quite clearly how to make the
> various formal techniques work together, by allowing the temporal
> parameter to 'float'. In fact, with a bit of extra work one can embed
> almost all the necessary temporal reasoning into a generalized unification
> algorithm which extracts temporal constraints during the unification
> process. I have all the details somewhere if you (or anyone else) are
> interested.
>
> Pat
>
>
> On Jan 27, 2011, at 11:19 AM, Ian Bailey wrote:
>
>> Thanks John,
>>
>> So in a 3+1 approach, when they actually "cut some ontology code", if
>> I've
>> understood you correctly, I'm guessing they timestamp the properties and
>> relationships ? This contrasts with a 4D approach where the Individual
>> is
>> sliced up into temporal stages and the properties are associated with
>> the
>> stages (apart from those properties that apply to the whole-life
>> individual).
>>
>> If I've got that right, then 3+1 is the approach the oil and gas folks
>> used
>> in late 80s early 90s on EPISTLE and the first drafts of ISO10303-221.
>> Am I
>> in the right ball park there ? Matthew ?
>>
>> Cheers
>> --
>> Ian
>>
>> -----Original Message-----
>> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
>> [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of John F.
>> Sowa
>> Sent: 27 January 2011 17:05
>> To: ontolog-forum@xxxxxxxxxxxxxxxx
>> Subject: Re: [ontolog-forum] 3D+1 (was presentism...was blah blah blah)
>>
>> On 1/27/2011 11:17 AM, Ian Bailey wrote:
>>> I get 4D, finally, after years of hanging on Chris and
>>> Matthew's coattails, but the 3D+1 thing is a mystery.
>>
>> The basic issue is the definition of a physical object
>> and its relationship to a privileged time called 'now':
>>
>> 1. In 3+1 D, which is the implicit assumption in ordinary
>> language, an object (human, animal, plant, or artifact)
>> comes into existence at some time t1 (e.g., birth),
>> ceases to exist at some time t2 (e.g., death), and
>> for each now between t1 and t2, all parts of it
>> exist together now.
>>
>> 2. In 4D, a physical object extends over a 4D volume, whose
>> lower and upper time coordinates are t1 and t2 and whose
>> spatial coordinates trace out a volume that spans the
>> object's travels.
>>
>> 3, In 3+1 D, the object undergoes various changes, which
>> cause some properties to become true or false at different
>> times called now.
>>
>> 4. In 4D, the object doesn't change, but it has time-dependent
>> parts (slices or stages) at which various properties may be
>> true or false.
>>
>> The analogy I prefer (since I studied fluid mechanics at one
>> time in my life) is between Lagrangian and Eulerian coordinate
>> systems for representing and computing fluid flow:
>>
>> 1. Lagrangian coordinates are like a 3+1 D system: the
>> observer follows a particular parcel of fluid as it moves.
>>
>> 2. Eulerian coordinates are like a 4D system: the observer
>> sits on the side and watches the flow of all the fluid
>> as a whole.
>>
>> In our ordinary language, we talk about our bodies in Lagrangian
>> terms. We observe our own motion through space and time, and
>> relate everything else to where we are *now*.
>>
>> An Eulerian system is like a God's eye view of the universe.
>> God sees everything spread out in all dimensions of space
>> and time. There is no privileged point of time or space.
>>
>> John
>>
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"I speak as an American to the leaders of my own nation. The great
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