Re: constraints in algebra instead of calculus
From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 23 May 2007 14:27:38 GMT
Message-ID: <ubY4i.212893$aG1.147055_at_pd7urf3no>
>
>
> Sometimes it makes them more succinct. There is danger, however. I don't
> think it's decidable how a constraint defined on an arbitrary view affects
> the closure of the set of constraints on the database schema. Can a
> constraint defined on a view always be a logical consequence of a set of
> constraints defined on the underlying base relations? I don't think so.
> ...
Date: Wed, 23 May 2007 14:27:38 GMT
Message-ID: <ubY4i.212893$aG1.147055_at_pd7urf3no>
Brian Selzer wrote:
> "paul c" <toledobythesea_at_oohay.ac> wrote in message
> news:nnM4i.206459$DE1.56863_at_pd7urf2no...
>
>>Brian Selzer wrote: >> >>>... >>>V is not in BCNF: since StaffId --> CourseId in Teaches, StaffId --> >>>CourseId in V. >>>... >> >>I'll think about your other points, it could be that I misunderstood his >>point - meanwhile, I must say I'm not too concerned about V's 'form' as I >>think he used it just to make his exposition clearer - in a suitable >>language, I would guess, one would not be forced to define a view in order >>to express the constraint. >>
>
>
> Sometimes it makes them more succinct. There is danger, however. I don't
> think it's decidable how a constraint defined on an arbitrary view affects
> the closure of the set of constraints on the database schema. Can a
> constraint defined on a view always be a logical consequence of a set of
> constraints defined on the underlying base relations? I don't think so.
> ...
p Received on Wed May 23 2007 - 16:27:38 CEST