Re: SUPPORT FOR DECLARATIVE TRANSITION CONSTRAINTS

On Sep 19, 9:19 pm, paul c <toledobythe..._at_oohay.ac> wrote:
> On 18/09/2010 6:42 PM, Brian wrote:
>
> > The work order number is an element of both candidate keys, so both
> > keys differ as a result of the supervisor's update.  How would it
> > be possible to match the tuple in the relvar as it was prior to the
> > update under consideration to the tuple in the relvar as it would
> > be after the update to verify that LBRDATE isn't
>
> As far as I know, the only way a tuple can have 'before' and 'after'
> values is to believe in mystical mutant tuples.

Please go back to school and take an introductory course in logic.

Tuples are supposed to represent propositions. Propositions refer to objects in the universe of discourse. In the context of database updates, it is a gross oversimplification to assume that the universe is nothing but a collection of arbitrary objects that are independent of time. Transitions have a location in time, and some of the objects in the universe must have a location in time, otherwise there could only ever be one database--that is, one true account of the universe-- for all time. The universe must therefore consist of two distinct sorts of objects: abstract objects that are indeed independent of time and concrete objects that aren't. Concrete objects can have a location in time, which means that they can come into existence, possibly change in appearance, and cease to exist. A proposition that can be true at one time and false at another must have at least one concrete referent. Again, tuples are supposed to represent propositions. Is it so difficult to grasp that two different propositions at different times can reference the same concrete object? And by extension, is it so difficult to grasp that it should be possible to match tuples in a relvar as it was prior to an update to tuples in the database as it would be if the update were to succeed? Received on Mon Sep 20 2010 - 10:40:41 CEST