Re: object algebra

"Neo" <neo55592_at_hotmail.com> wrote in message news:4b45d3ad.0402231509.48edf2a0_at_posting.google.com...
> > > "Codd now regards NULLs as an integral part of RDM".
> >
> > Codd was wrong in that statement,
>
> Codd is correct that NULLs are required in RDM, unless all your data
> fits neatly in rectangular tables which is not the general case, or
> unless one resorts to unpractical methods such as generic modelling
> (ie all data in one table with one column).
>
> > and many relational proponents support the non-use of nulls.
>
> The occurence of NULLs when applying RDM in the general case doesn't
> depend on what proponents support. It depends on the model.

And the model says no nulls, or at minimum says nothing about them. They violate relational closure in many ways, so that would tend to imply they're not allowed. Codd was, with all due respect, wrong about the utility of nulls.

• Eric