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Re: Define "flatten database" ?

From: David Cressey <dcressey_at_verizon.net>
Date: Sat, 25 Feb 2006 20:54:00 GMT
Message-ID: <It3Mf.551$v34.272@trndny02>

"Mark Johnson" <102334.12_at_compuserve.com> wrote in message news:hjd1021r1i12pggg356d78t16f2g2a7rb7_at_4ax.com...
> "David Cressey" <dcressey_at_verizon.net> wrote:
>
> >define a "relational table" as the representation of a relation in a
relational database.
> >Describe an "SQL table" as an approximation to a relational table. Move
on
> >from there.
>
> That paper of Codd's that I quoted in a couple of messages showed his
> desire to even replace the idea of the table/relation correspondence
> with that of a table/relationship.

Were you quoting from the 1970 paper? If so, the paper is clear about the difference between a relation and a relationship. In a relationship, the attributes are specified by name rather than by order. And Codd gives a motivation for doing things this way. It's a burden on the user, Codd says, to make the user remember the order in which a tuple of degree 30 or so specifies its values. I agree with that.

> If the tuples were not always in
> order, as they are in picking elements from successive sets in the
> theory, then he perhaps felt uncomfortable still terming a table based
> on that, a relation. Thus, terminology. Once you move from the theory
> to the implementation, everything else can change, as well. And as
> things are changed on the working side of it, perhaps the connection
> with the theory grows more tenuous. If that poses problems, then that
> can be stated.

> If it both solves and causes problems, so too. Of that,
> the use of self-referential tables is pretty much the example of the
> moment,

The use of self referential tables is explicitly not ruled out in the 1970 paper.
and such use of Connect By, or similar.

I don't wish to get involved in the religious wars over the use of "Connect by". I clearly recognize it as an Oracle specific construct. But I don't hesitate to use it whenever I think it convenient. The nested set model is also very clever, and very useful. I don't hesitate to use it when I think it's convenient. Received on Sat Feb 25 2006 - 14:54:00 CST

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