Re: Smart Database Tricks

From: Jan Hidders <>
Date: Fri, 22 Jun 2007 12:54:59 -0000
Message-ID: <>

On 22 jun, 14:25, Bob Badour <> wrote:
> Jan Hidders wrote:
> > On 22 jun, 01:36, Bob Badour <> wrote:
> >>Jan Hidders wrote:
> >>>On 21 jun, 21:17, vldm10 <> wrote:
> >>>>On Jun 18, 7:41 pm, Jan Hidders <> wrote:
> >>>>>On 18 jun, 20:59, vldm10 <> wrote:
> >>[snip]
> >>>>>If this is a relation then
> >>>>>all columns are attributes and since you have represented all the
> >>>>Can you please, tell me what is the definition of the attribute in RM.
> >>>It's a column of a relation. Conceptually it represent the role in the
> >>>predicate that is represented by the relation.
> >>Is an attribute a predicate variable of some sort?
> > As in "the x in predicate P(x, y) "? Yes, I'd say that is the same
> > thing.
> I thought so. When one writes a query and requests certain attributes,
> would those requested attributes be free variables in a logic sense?

That's not how I would formulate it. Strictly speaking the attribute is a position or role in a predicate. So if the predicate is P(x, y) then there are two positions / attributes: the first position where x is bound and the second position where y is bound. It doesn't really make sense to say that the variable is the attribute because how then would you describe the situation in the formula "P(x, y) and Q(x, x)"? Is the variable 'x' an attribute? It makes more sense to say that it is a variable that is bound to the first position / attribute of P and the first and second posiiton / attribute of Q.

So, er, I guess my previous answer should actually have been "no, not exactly". ;-)

  • Jan Hidders
Received on Fri Jun 22 2007 - 14:54:59 CEST

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