Dear Pat, (01)
You wrote:
>I will try to sketch the argument, though I would hesitate to call it
>a proof. It amounts to defining a syntactic transformation from one
>ontological formalism style to another, and then observing that one of
>these can reasonably be seen as a formalism of the 4D picture, and the
>other of the 3D one. The basic point is that there are only two ways
>to insert a time parameter into a 'static' description: it either gets
>attached to a relation name as an argument, or to an individual name,
>converting them to a term. One writes either (R a b t) or (R (a t)(b
>t)). The first is naturally read as a continuant-style description,
>using time-dependent fluents to talk of things whose identity is
>considered to be timeless, the latter as a 4D one, in which assertions
>are made timelessly about 'slices' of a 4D entity. (There are other
>ways, but they all involve changing the logic in some way, eg by
>adding temporal contexts or tenses.) Basically, and oversimplifying
>things greatly, one can convert from 3D to 4D and back by 'moving' the
>temporal parameter between these two positions. This is an observation
>about the formal notation, of course, but the philosophy is basically
>irrelevant until it gets cashed out in a formal expression of some
>kind. Whatever your views are on property instances, in particular,
>can (if they are relevant to the final ontology) be ultimately
>expressed in one of these ways, and when it is so expressed, can be
>almost mechanically transliterated into the other, and from there
>'read back' as being about the other kind of temporal entities. I
>realize that this hardly constitutes a philosophically valid form of
>argumentation, but then of course we are not here doing philosophy,
>but rather ontology engineering: right? (02)
This is how I see it too. Some further thoughts are: (03)
1) Consider a test to determine material properties. During the test, the
test machine - test specimen assembly goes through a succession of states.
For these states, time (since the beginning of the test), crosshead
displacement, extensometer displacement and force are measured. (04)
- The 4D approach defines the states as different objects, and records time,
crosshead displacement, extensometer displacement and force for each.
- The 3D approach records crosshead displacement, extensometer displacement
and force as time varying relationships with the whole life of the test
machine - test specimen assembly. (05)
The 3D approach would be convenient if we were principally interested in the
variation of these measurements with time. However, we are principally
interested in the variation of force with extensometer displacement. The
variation of force with time or extensometer displacement with time is
secondary, but both need to be kept within limits. The 4D approach has been
adopted by the test machine manufacturers for their output format. (06)
2) There is a problem with "slices" - both temporal and spatial. Naive
models assume that relationships exist for a material object at an instants
in its life and for a point within it. Consider the variation of density
with time and space within a fluid - something that fluid dynamicists worry
about. (07)
But density is not defined at a point. A description of the variation of
density from point to point within a body requires a specification of scale.
This is not an academic issue when describing complicated composite
materials. There are similar problems with properties which purport to be
defined for an instant. (08)
Future ontologies which recognise scale when considering instants in time or
points in space, may shed some light on the 3D/4D issue. (09)
Best regards,
David (010)
============================================================
David Leal
CAESAR Systems Limited
registered office: 29 Somertrees Avenue, Lee, London SE12 0BS
registered in England no. 2422371
tel: +44 (0)20 8857 1095
mob: +44 (0)77 0702 6926
e-mail: david.leal@xxxxxxxxxxxxxxxxxxx
web site: http://www.caesarsystems.co.uk
============================================================ (011)
_________________________________________________________________
Message Archives: http://ontolog.cim3.net/forum/uom-ontology-std/
Subscribe: mailto:uom-ontology-std-join@xxxxxxxxxxxxxxxx
Config/Unsubscribe: http://ontolog.cim3.net/mailman/listinfo/uom-ontology-std/
Shared Files: http://ontolog.cim3.net/file/work/UoM/
Wiki: http://ontolog.cim3.net/cgi-bin/wiki.pl?UoM_Ontology_Standard (012)
|