Re: SUPPORT FOR DECLARATIVE TRANSITION CONSTRAINTS

On 27/09/2010 4:29 PM, Brian wrote:
>> You have this irresistibe urge to regard tuples as mutable,
> Not so. Tuples are not mutable, but the referents of the propositions
> they represent may be.
>
> Consider a database in which every tuple has to have as one of its
> components the time of the last transition. Suppose now that there is
> a database update. In the update, every tuple is replaced, because
> every tuple has to have as one of its components the time of the last
> transition, which is now the time of the update under consideration.
>
> The employee named paul c at time t1 was being paid $43/hour.
> The employee named paul c at time t2 was being paid $37/hour.
>
> Are "the employee named paul c at time t1" and "the employee named
> paul c at time t2" the same employee at different times, or are they
> different employees at different times. In other words, did the
> employee named paul c take a cut in pay, or are the employees named
> paul c at t1 and t2 completelyh different employees?
>

Either could be true. We can't tell from either tuple. It might be that some user could tell because, say, he knows that no one has quit or been fired lately or because of some other knowledge not recorded. I don't think it would matter whether or not the transition was a key component, but in any event I'd still clean the toilets for 37 bucks per hour. Received on Tue Sep 28 2010 - 03:02:07 CEST