Re: Surrogate Keys: an Implementation Issue
Date: Sun, 30 Jul 2006 18:27:38 GMT
Message-ID: <uS6zg.277668$Mn5.79454_at_pd7tw3no>
Brian Selzer wrote:
> "paul c" <toledobythesea_at_oohay.ac> wrote in message
> news:yw4zg.281148$IK3.258613_at_pd7tw1no...
>> Brian Selzer wrote: >>> "paul c" <toledobythesea_at_oohay.ac> wrote in message >>> news:zTOyg.269253$IK3.233927_at_pd7tw1no... >>>> Brian Selzer wrote: >>>>> "paul c" <toledobythesea_at_oohay.ac> wrote in message >>>>> news:g9Nyg.263082$iF6.250988_at_pd7tw2no... >>>>>> Brian Selzer wrote: >>>>>>> What's the point of a database if it doesn't reflect some aspect of >>>>>>> reality. ... >>>>>> To talk precisely about whatever we want to talk about. Nothing more. >>>>>> Doesn't need to be real. >>>>>> >>>>> Agreed. But even a conceived universe subsumes certain absolutes, such >>>>> as time. >>>>> >>>> In that case, the statements in the database should talk about time, >>>> ie., aspects of time. These are different from statements about the >>>> time it takes the database to say something. >>>> >>> There can be no discussion without time. Relational assignment cannot >>> exist without the concepts of before and after. And the truth of a >>> statement belonging to the database state that existed before an >>> assignment depend on the circumstances that obtain before the assignment, >>> which may no longer remain after. >> No, it doesn't depend on 'circumstances'. Assuming variables, as you are, >> the truth of a statement depends on the value of the relation that is >> assigned to a variable. >>
>
> I don't understand. If I make a true statement, "I am at work.," and then
> drive home, then that statement is no longer true because the circumstances
> changed. Consequently, "work" must be changed to "home" in order for the
> statement to remain true.
>
>> p
>
>
I thought we were talking about what we do to databases, not the circumstances of your drive home. You seem to think that the db must magically know that you can't be at home unless you were previously at work. It can only show an abstraction of that and then only if you choose to define specific predicates for the arbitrary choice of wanting to describe other circumstances than merely your present location, say, 'arrivals' and 'departures'. If your "true statement" is "I am presently at work" then its predicate is something like "PresentLocations". It is your choice of predicate that has introduced time to your application, not the RT.
p Received on Sun Jul 30 2006 - 20:27:38 CEST