Re: 4 the FAQ: Are Commercial DBMS Truly Relational?

"Laconic2" <laconic2_at_comcast.net> wrote in message news:GoadnX8cvMul6vTcRVn-iw_at_comcast.com...
>
> "Marshall Spight" <mspight_at_dnai.com> wrote in message
> news:xMcad.156343$wV.96061_at_attbi_s54...
>
> Two points: first, the empty set carries the same kind of information that
> a NULL in anouter join does, without being a NULL.

Exactly!!!

One big beef I have with NULLs: their meaning is overloaded. Is it "missing?" Is it "not applicable?" If we take the approach of not having a special NULL, but instead allow zero-cardinality things, and also allow the creation of, say, enumerated types, then the data model can model whatever it needs to, and the algebra can stay pure.

> Second, in order to accept the result as a relation, you have to allow
> domains that are relations. Since Date does this, it's consistent with the
> direction he's going in.
>
> It looks interesting. Thanks for clearing it up.

My pleasure.

Marshall Received on Sun Oct 10 2004 - 21:32:34 CDT