RE: SUO: RE: Re: More KIF-ified Ontology Content
>Dear Matthew,
> . Thanks for this explanation. I certainly agree about
>the restrictions with 3D models
>
> . However, I still don't understand why relations do not also
>have a time dimension. For example, what about two beings which have
>friendly relations at some periods and hostile ones at other times?
In the 3d (actually 3.5d would be a better way to put it) ontology
one might write
(Friendly A B t1) and (not (Friendly A B t2))
or maybe
(Holds (Friendly A B) t1) and (not (Holds (Friendly A B) t2)).
In the 4d ontology one distinguishes the 'parts' of each person at
the relevant times - thinking of people, like everything else in this
ontology, as extended through time and so having 'temporal slices' -
and then would write something like:
(Friendly A@t1 B@t1) and (not (Friendly A@t2 B@t2)
where X@Y means the temporal Y-slice of the thing X. The relations
are now timeless (they don't have a temporal parameter and they don't
hold at one time but not at another), but the things themselves are
temporally indexed. For more details of the various possibilities,
take a look a the discussion in
http://www.coginst.uwf.edu/users/phayes/TimeCatalog1.ps
The advantages of this framework can be best appreciated by tryi ng
to use it to axiomatize things like machinery and liquid flow. For
example, it gives one the ability to talk about the temporal 'shapes'
of various actions, and distinguish velocities from accelerations,
etc.. The disadvantages are more subtle, and include the fact that it
is just as easy to write things like
(Friendly A@t1 B@t2)
which are at best odd and at worst meaningless. CYC uses a basic
temporal framework of this sort, and it enriches it with a lot of
relational categories which are designed to rule out oddities like
this, such as 'isotemporal' relations which are required to only hold
between things which exist during the same time interval. There are
other complications as well concerned for example with concepts which
intrinsically involve certain kinds of change, such as divorce. (If
marriage is isotemporal, then the death of a spouse ends the
marriage, but it doesnt make the surviving spouse a divorcee.)
Pat Hayes
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