Re: relations aren't types?

"Marshall Spight" <mspight_at_dnai.com> wrote in message news:cNKHb.64146$VB2.125134_at_attbi_s51...
> "Bob Badour" <bbadour_at_golden.net> wrote in message
news:MPOdnepoTvzeP3OiRVn-hA_at_golden.net...
> >
> > Sorry. Time is just as atomic as any other type including relation
types.
>
> I'm not clear on why types have to be atomic. I have not seen a
> reason for it.

It is not a question of whether they have to be. They just are. The value 5 does not change when we represent it as 5+0j where j is the imaginary unit.

> > > Agreed. Would you object to a relation with an attribute of type
> > > Alpha?
> >
> > I cannot remember: Is alpha the type with an empty set of values and the
> > entire universe of operations? Or is alpha the type with the entire
universe
> > of values and the empty set of operations?
>
> Allow me to suggest a mnemonic: alpha is the first letter in the greek
> alphabet; it is at the "top" of the sequence. Omega is the last letter;
> it is at the "bottom" of the sequence. Alpha corresponds to what
> lattice theory calls "top" and omega to "bottom." Alpha/top is the
> maximal superclass in the type lattice; it has all values in it.
>
> Alpha/top as an attribute type has some modest usefulness in cases
> of extreme genericity. Omega/bottom as an attribute type means
> the relation could never have any rows, which distinctly limits
> its utility.

Alpha as an attribute type means the user cannot perform any operations on the values, which distinctly limits its utility too; although, not as much as omega.

As I said, I have no objection to these types in relations. I see no purpose for either of them as attribute types in relvars. Received on Mon Dec 29 2003 - 06:21:33 CET