Re: Data independence

"x" <x-false_at_yahoo.com> wrote in message news:<40a35391_at_post.usenet.com>...
> **** Post for FREE via your newsreader at post.usenet.com ****
>
>
> "Alfredo Novoa" <alfredo_at_ncs.es> wrote in message
> news:40a34518.331576_at_news-read3.maxwell.syr.edu...
> > On Thu, 13 May 2004 11:46:22 +0300, "x" <x-false_at_yahoo.com> wrote:
> >
> > >
> > >
> > >
> > >> It is possible to write applications that are independent of
> > >> the change of key constraints in a RDBMS ?
> > >
> > It does not make sense to me.
> >
> Suppose you have an application that use some relvars like this:
> R(A1,A2,A3,A4,B1,B2,B3,...)
> where {A1,A2,A3} is a candidate key for R.
> After some time you find out that {A1,A2,A3,A4} is the "real" candidate key
> for R.
> Do you need to modify the application ?
> There is a way of writing applications that are not affected by this change
> ?

   No.    

   But let me put this to you: your use of the relational model has given  you a language to describe the problem, and to analze the impact on  applications that such a change will have. You can instantly decide  when a particular query needs to be re-written (any query that employs  the previous Key constraint).

   How would you analyze a procedural routine to arrive at the same  conclusion? In a related question, how would you decide that the  sub-routine halts? Received on Thu May 13 2004 - 19:08:54 CEST