Re: RM and definition of relations/tuples

"Martin Zapf" <Martin_Zapf_at_gmx.net> wrote in message news:dm6q50$5i3$1_at_online.de...
> JOG wrote:
> > Martin Zapf wrote:
> >
> >>1. defintion:
> >>
> >> A relation r for schema R is a mathematical relation (cartesian
> >> product) over the
> >> domains from the attributes of R.
> >> So r:=dom(A_1)xdom(A_2)x...xdom(A_n)
> >> A tuple is an element of r.
> >>
> >
> >
> > out of curiosity does this first definition originate from? Definition
> > 2 certainly seems on the money to me, but in the first definition I see
> > no mapping from value to attribute - this would seem essential to me
> > given such a mathematical formalisation (attributes can't be
> > automagically known externally to a system which presupposes that they
> > may vary?).
> >
> > All best, J.
> >
>
> You can find the first definition in various books, for example in
> 'Database System Concepts, Silberschatz' or 'Fundamentals of Database
> systems, Elmasri'.
>
> In the first definition is a littel typo: relation r should be a subset
> of the cartesian product dom(A_1)xdom(A_2)x...xdom(A_n).

> To map the values of one tupel (element) of relation r to the attributes
> you have to consider the order of the attributes in the cartesian
> product which r is a subset from.
> I also must admit that this definition is not satisfying for me.

How you define the cartesian product ? Received on Fri Nov 25 2005 - 12:47:06 CET