Re: some ideas about db rheory

On Jul 27, 7:46 pm, rp_at_raampje.(none) (Reinier Post) wrote:
> I wrote:
> >> [...] if you have no way to track identity across changes
> >> in real life, adding it as a modeling feature (either with explicit
> >> identities or by distinguishing between updates and deletes+inserts,
> >> as Brian proposes) isn't going to help a bit.
>
> Brian replies:
>
> >[...]   Either there can be change, which implies that there can be
> >things that can change, or there cannot be change, which means that
> >there cannot be deletes or inserts, let alone updates.
>
> No, Brian.  These deletes, inserts, and updates are about statements
> of fact about the world, which can change to reflect new or changed
> observations, even when we haven't identified any objects that these
> statements are about to the extent you appear to deem necessary.  I can
> observe Mary's goldfish and its medical condition, and truthfully record
> that in my database, two days in a row, *regardless of* whether I can
> tell whether we're dealing with the same goldfish in both cases.

Either there can be change, which implies that there can be things that can change, or there cannot be change, which means that there cannot be deletes or inserts, let alone updates. Deletes, inserts and updates are not about statements, they are themselves statements that assert what is different and how it is different; therefore, if there cannot be change, then nothing can be different and thus there cannot be any deletes, inserts or updates. The implication is that if there cannot be change, then there can be absolutely no relationship between databases at different times, so the concept of deleting would not make sense, for it assumes a relationship between databases, neither would that of inserting, and most definitely not updating.

Your argument neither affirms or denies my statement. What it does is illustrate the fact that descriptions, such as "Mary's goldfish," can refer to different things at different times in the same way that a particular instance of a composite key can refer to different things at different times--something I've been arguing for a long time. Because interpreters are temporal beings, interpretations must occur / at a time/, which requires that there must be different interpretations at different times. Even under the possible worlds paradigm, only one possible world at a time can be the actual world.

>
> We may choose not to care and it won't be a problem.
>
> But for goldfish, at least we know they are identifiable in principle.
> This is not so easy for other types of objects; say, species of fish,
> countries of the world, or clouds.
>
> >Once you
> >commit to change, a system that has no way to track identity across
> >changes is broken.
>
> If you mean: once you commit to being able to identify objects
> across changes, you're right.  But it becomes a rather tautological
> statement.

If there can be change, then there can be things that can change; therefore, once you commit that there can be change, you must accept that there can be things that can change. If there can be things that can change, but the system has no way to track identity across changes, then the system is broken.

>
> >For things that can change to be identical, the
> >loci in time or space during which they exist or existed must
> >coincide, and all changes in appearance that has been sustained by any
> >at any time must have been sustained by all at that same time.  There
> >can be no discernible difference between them at any time during their
> >lifetimes.
>
> I feel you keep confusing things and statements about things.

I am not.

> A relational database records statements, usually about things.

Statements are /always/ about things. Each term in a statement is assigned something--some...thing--under an interpretation.

>
> --
> Reinier
Received on Tue Jul 28 2009 - 15:09:53 CEST