Re: Does Codd's view of a relational database differ from that of Date & Darwin? [M.Gittens]

David Cressey wrote:
> "Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message
> news:Bkkqe.115913$qE.6759462_at_phobos.telenet-ops.be...
>

>>I'm not sure what it means to be an "inherent part of the theory" but
>>Codd describes non-simple domains as "undesirable" and in section 1.5 he
>>argues in favour of flat relations. This becomes even more clear if you
>>look at the articles that followed because, for example, the notion of
>>"relational completeness" (and the relationship with first-order logic)
>>doesn't make much sense if you allow nested relations.

The relational model is more a *prescriptive* theory than a *descriptive* theory. In such a context these words are not that far apart. Moreover, as a mathematical statement it would simply be wrong to say that nested relations are impossible.

I think one needs to be careful about reading the article too much from a modern perspective. The question about what is exactly *the* relational model that some here are so obsessed about, wouldn't have made much sense to Codd at the time. In fact, it still doesn't.

> What I'd be curious to know is whether it's an undesirable burden to place
> on the DBMS implementor, an undesirable alternative to place in the hands of
> the database designer, an undesirable avenue for further exploration of the
> theory, or something else.

They tend to lead away from the goal that is so important in large shared databases: data independence.

• Jan Hidders