Hi Pat, (01)
I liked the explanation until I came to
PH> 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 (02)
It may be true that they (sometimes?) use a 3D+1 style when writing their
logic. But I am not sure they would interpret this as "object terms are
still thought of as denoting 3D rather
> than 4D entities." What I have always understood is that the OBO
continuants are not really best understood as have a particular 3D (spatial)
extension - maybe best as not having any dimensionality at all - maybe to
show that the way they have spatial and temporal attributes is different it
would better be called a 0+3D+1D approach. (03)
I suppose you will say this is a classification of syntax not metaphysics -
but then maybe it would be better to just describe the syntax and leave 3D
and 4D out of it entirely. (04)
Also, surely @): R(a@t, b@t) is not the only or even the best syntax for a
4D approach. Do I need any time parameters to say 'the first act of the play
is part of the play'. I wonder what syntax the OBO guys use for their
occurrents. Is it always this style? (05)
Regards,
Chris (06)
> -----Original Message-----
> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-
> bounces@xxxxxxxxxxxxxxxx] On Behalf Of Pat Hayes
> Sent: 03 February 2011 09:38
> To: ian@xxxxxxxxxxxxxxxx; [ontolog-forum]
> Subject: Re: [ontolog-forum] 3D+1 (was presentism...was blah blah blah)
>
> 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.
>
> 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. 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.
>
> 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. 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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