Re: The Fact of relational algebra (was Re: Clean Object Class Design -- What is it?)

From: Jan Hidders <hidders_at_REMOVE.THIS.win.tue.nl>
Date: 5 Oct 2001 12:35:22 GMT
Message-ID: <9pk9ea$453$1@news.tue.nl>

Daniel Poon wrote:
>
> "Leandro Guimarães Faria Corsetti Dutra" <leandrod_at_mac.com> wrote in message
> news:3BBBBEEE.30906_at_mac.com...
> > > I seem to remember the rdbms guys redefined 'completeness', to
> > > something that has no bearing on mathematical compeletness (which
> > > I cant remember the

>>

> > Can you expand on that?
>
> I think completeness means that the language can express any
> 'computable function'. For example, it can express the square of a
> number, since that is computable.

And that is roughly also how the "RDBMS guys" define it. The completeness that is associated with the relational algebra is usually qualified such as "relationally complete" or something similar.

> > What "fundamental concepts" do you think that relational algebra
> > redefines?
>
> I found this definition of "relation" on a maths page on the net:
>
> *** relation : (logic, set theory)
> a correspondence between two sets (say A, B) represented by
> a set of ordered pairs, each containing one element from
> A and one from B.
>
> Implying you have to normalise everything into binary relations before it
> looks anything like the above definition.

Yes, for a big part of mathematics binary relations are sufficient, but their generalization, n-ary relations, was already quite common before the relational model was introduced.

-- 
  Jan Hidders

Received on Fri Oct 05 2001 - 07:35:22 CDT