Re: More on lists and sets

Brian Selzer wrote:

>

NFNF models do not necessarily introduce redundancy. And neither is the logic that is required to deal with them a problem. Note that just as we only use a restricted subset of first-order logic for the flat relational model, you would also only use a restricted subset of second-order logic fo the nested relational model, and the prevents any theoretical problems.

> Issues that are solved through the application of
> higher normal forms reappear with the introduction of composite attributes.

Such as? In fact, the reverse true. It is for example known that in some cases normalization to BCNF while being dependency preserving is not possible in the flat model, but is in fact possible in the nested relational model (given appropriate generalizations of dependencies and normal forms).

> The predicate of a NFNF relation may include variables that range over
> subsets, which cannot be expressed using first order logic. I think that
> this makes it much more difficult to verify the correctness of the model.

You can express a larger class of constraints and some of those are indeed hard to verify, but since the alternative is to not express them at all and the old ones are still just as hard to verify, I find it hard to see that as a problem.

• Jan Hidders