Re: RM VERY STRONG SUGGESTION 4: TRANSITION CONSTRAINTS

On Sep 9, 6:10 pm, r..._at_raampje.lan (Reinier Post) wrote:
> Brian wrote:
> >As Codd has written, and as Bob Badour continually asserts every time
> >the subject of surrogate keys comes up: Every key is a surrogate.
>
> Not in my terminology.
>
>
>
> >A surrogate for what?  For an object in the microworld being modeled.
> [...]
> >If that doesn't constitute a mapping, then perhaps you can enlighten
> >me as to what does.
>
> You're right that a mapping is intended, but it is
> outside the database and not usually completely defined.
> People or applications may turn out to have conflicting mappings
> for the same database table.
>

It doesn't need to be completely defined. What's important to this discussion is not the exact mapping but the fact that there is a mapping and the characteristics that are common to all objects that tuples in the database map to.

Think, for a moment, about the objects in the microworld. Are they just arbitrary abstract objects that are independent of time, or are they arbitrary concrete objects that can have arbitrary locations in time? If they're abstract, then neither do they change nor does the microworld. They are necessarily independent of time. There is no need for database updates: nothing ever changes because nothing ever can! There can only ever be one account of the microworld. If, on the other hand, the objects in the microworld are concrete, then when they do occur it is either at-a-time or during an interval in time. The contents of the microworld changes over time as what can be the case becomes what is the case. There are many true accounts of the database, but each holds true only during intervals in time bounded by the times that changes occur, and only one holds true during each of those intervals.

I contend that an arbitrary microworld is a combination of both arbitrary abstract objects and arbitrary concrete objects. The domains from which the components of tuples are drawn consist entirely of abstract objects that are independent of time. These must be independent of time because domains do not change, nor do elements of domains. But the extensions of the database predicate are collections of propositions whose referents must be concrete objects because the database can be different at different times. The truth values of those propositions depend first upon whether its referent has come into existence--that is, does the start of the interval during which the referent occurs fall before the instant of interpretation? Once it has been established that the referent has at some point come into existence, then a judgement is made as to whether or not the referent exemplifies the predicate at the instant of interpretation.

Whether people or applications turn out to have conflicting mappings for the same database table does not alter the fact that the referents of the propositions represented in the database must be concrete and therefore can occupy a location in time. Received on Fri Sep 10 2010 - 03:36:19 CEST