Re: Temporal database - no end date

On Jan 22, 7:40 pm, "David" <davi..._at_iinet.net.au> wrote:
> Marshall wrote:
>
> > There is one area in particular that is of the utmost
> > importance. The one overriding limitation on the logical
> > level that the physical level applies is that it must exist.
> > Any logical model that is not implementable is not worth
> > much.
>
> You need to qualify that, because as stated it implies that the reals
> (as a logical model) is not worth much.
>
> It is common for logical models to ignore physical limitations, making
> them impossible to implement. Proofs of correctness often depend on
> pure logical models. For example, a stack that never overflows is a
> useful abstraction. The Turing machine with its infinite tape is
> another useful abstraction.

Hmmm. Well, that is not how I use the terminology, but perhaps this is my mistake. I wouldn't call the reals a logical model. (What are they a model *of*?) Rather I would describe them as an abstraction, but I suppose "abstraction" and "model" are similar concepts.

What say, c.d.t.? Are the reals a logical model?

Anyone have a good pointer to a definition of conceptual, logical, physical?

> My point is only that it's the underlying logical model of the reals
> that allows us to make sense of what floating point numbers are all
> about.

Again, the phrasing is odd to me, but yeah, definitely.

Marshall

PS. I would have replied sooner, but you know, Heroes was on. Received on Tue Jan 23 2007 - 17:51:02 CET