Re: boolean datatype ... wtf?
Date: Wed, 29 Sep 2010 07:13:02 -0700 (PDT)
Message-ID: <8199e9e1-3f3c-43ce-9e20-8ed5e129d228_at_26g2000yqv.googlegroups.com>
On Sep 29, 9:46 am, paul c <toledobythe..._at_oohay.ac> wrote:
> On 29/09/2010 4:51 AM, Paul Mansour wrote:
> ...
>
>
>
> > What is the problem with a Boolean data type?
> > .
> > It is fundamental - so fundamental that in TTM it is the only
> > required scalar data type: “We require that at least one built-in
> > scalar type be supported : Namely, type “Boolean” (BOOLEAN in Tutorial
> > D”).
>
> > Date and Darwen go on to give the obvious reasons for this.
>
> > The fact that DEE and DUM may be interpreted as TRUE and FALSE is not
> > relevant. The result of A=B or A>B is not a relation.
>
> Aren't A=B and A>B relations?
I was under the impression that they are not, even if A and B are
relations. But I may have misintepreted C.J. Date on this.
In "Database in Depth" he writes:
"In Chapter 2, I mentioned the fact that the equality comparison
operator "=" applies to every type. In partitular, therefore it
applies to relation types.... Now I must immediatly explain that these
opeartors are not relational operators as such -- that is they are not
part of the relational algebra-- because their result is a truth
value, not a relation."