Re: Proposal: 6NF

David Cressey wrote:
>
> Agree with dawn. When I first learned set theory, they used the words
> "group" and "field" to describe
> a set with one or two operators defined on it. The word "set" does not,
> AFAIK, imply any operations.

But it doesn't exclude their existence either. You can construct a set that models the Reals and then after that construction define the operations that model the usual operations over the Reals. As long as their combination satisfies the laws that are given by the standard abstract definition of the Reals I claim that it is fair to say that you have corectly modeled the Reals. Val seems to disagree.

This is very relevant in the context of database theory because this is what one would do when presenting a formal model that describes the context of a database model: you define several sets that are your domains (Strings, Booleans, Integers, Rationals, Floats) and in addition you define operations over them (+, *, length, ...). Note that these function are often cross-domain (e.g. length: String -> Integer) and cannot be really said to belong to one domain or another.

Does that make sense to you?

• Jan Hidders