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From: Donal K. Fellows on 22 Nov 2009 19:24
On 22 Nov, 20:59, "tom.rmadilo" <tom.rmad...(a)gmail.com> wrote:
> The class of an object does not change, but the instance properties of
> the predicate might change.
>
> For instance, I might sell my chair to someone else. Instead of
> removing the previous (Me<->Mine<->Chair) relationship, I modify the
> Mine predicate to include a time interval and create a new
> relationship (Me2<->Mine2<->Chair). Somewhat by accident I have
> created a history of ownership of the Chair.

Perhaps. It's a difficult area, because when you combine description
logic (the natural model for class/object relationships) and temporal
logic (the way to characterize statements about things that change)
you get a logic that is intractable. I believe there are tractable
subsets (other than straight DL and TL), but this was an area where I
didn't pay that much attention; it's quite complex and I only really
know enough to know that this an area to be exceptionally careful (and
to call on expert help if necessary; a benefit of working in a
research university).

Donal.
From: tom.rmadilo on 22 Nov 2009 20:58
On Nov 22, 4:24 pm, "Donal K. Fellows"
<donal.k.fell...(a)manchester.ac.uk> wrote:
> On 22 Nov, 20:59, "tom.rmadilo" <tom.rmad...(a)gmail.com> wrote:
>
> > The class of an object does not change, but the instance properties of
> > the predicate might change.
>
> > For instance, I might sell my chair to someone else. Instead of
> > removing the previous (Me<->Mine<->Chair) relationship, I modify the
> > Mine predicate to include a time interval and create a new
> > relationship (Me2<->Mine2<->Chair). Somewhat by accident I have
> > created a history of ownership of the Chair.
>
> Perhaps. It's a difficult area, because when you combine description
> logic (the natural model for class/object relationships) and temporal
> logic (the way to characterize statements about things that change)
> you get a logic that is intractable. I believe there are tractable
> subsets (other than straight DL and TL), but this was an area where I
> didn't pay that much attention; it's quite complex and I only really
> know enough to know that this an area to be exceptionally careful (and
> to call on expert help if necessary; a benefit of working in a
> research university).

In theory certain, maybe most, problems will be intractable. But the
exposed nature of the structure means that there are many
opportunities to solve specific problems. Once solved, the solution
can be applied to similar problems.
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