Re: Proposal: 6NF

David Cressey wrote:
> "Jan Hidders" <hidders_at_gmail.com> wrote in message
> news:1161162871.923080.229180_at_i3g2000cwc.googlegroups.com...
> >
> > 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?
>
> Yes, except for one thing. I'm having trouble reconciling the word "domain"
> as you used it above, with the usage I'm accustomed to, as in "CREATE
> DOMAIN" from SQL.

Theoretically there is no reason to make a distinction between type and domain and as far as I know it is mainly there for historical reasons. I'm not a member of the SQL-is-evil club, but in this case I think it is fair to say that it uses two concepts where only one would have sufficed.

• Jan Hidders