Re: Stored fields ordered left to right

From: Dawn M. Wolthuis <dwolt_at_tincat-group.com>
Date: Sun, 11 Jan 2004 21:06:01 -0600
Message-ID: <btt2ut$jt6$1@news.netins.net>

"Adrian Kubala" <adrian_at_sixfingeredman.net> wrote in message news:slrnc03i64.ov7.adrian_at_sixfingeredman.net...
> Dawn M. Wolthuis <dwolt_at_tincat-group.com> schrieb:
> >
> > "Adrian Kubala" <adrian_at_sixfingeredman.net> wrote in message
> > news:slrnc01db2.k9f.adrian_at_sixfingeredman.net...
> >> Dawn M. Wolthuis <dwolt_at_tincat-group.com> schrieb:
> >> > With this discussion, I've been focussed on one specific issue,
> >> > where the database model I am using has been taken to task for not
> >> > employing relations. I have no problem stating that it does not
> >> > 100% follow a relational database model, however, this one point --
> >> > that it does not employ relations is entirely false.
> >>
> >> That's like calling a black and white camera a "color camera" because
> >> black and white are colors.
> >
> > Most certainly not. First of all, black and white are not typically
> > considered colors by color professionals, I believe.
> >
> > I will be the first to say that the Nelson-Pick model does not meet the
> > criteria of the relational database model. But it is absolutely the
case
> > (if you accept my analysis that it is based on functions, I think you
will
> > agree) that it is a mathematically relational model, right?

> It does not allow you to express *any* relation, therefore it is not
> relational, in exactly the same way that a camera which only lets you
> take pictures of pink is not a color camera. If your model let you
> express mathematical relations instead of "Codd relations", then I would
> agree with you, but since there are mathematical relations which your
> model cannot express, it's wrong to call it relational.

Every relation where each tuple has a unique identifier or candidate key can also be represented as a function. Can you give an example of a set of propositions that can be modeled as relations but not as functions? These functions are not limited to 1NF and, as such, typical propositions can be modeled much more handily than in a relational model. But if you can produce an example that can be expressed using relations and not functions or that is even easier to work with when represented as relations rather than functions, I am VERY interested.

> Especially since it seems your intent in doing so is to imply that it is
> just as expressive as the relational model, when in fact it is strictly
> less expressive. (Not to imply any value judgement, but simply to convey
> the fact that there are relations which your model cannot possibly
> express but any relational model can, whereas any function that your
> model can express, any relational model can as well.)

Yes, you are right that I intend to state that it is just as expressive, but no, it does not simply follow from the statement that it uses functions that it is more expressive. I will try not to jump steps like that. I think you are incorrect in assuming that functions are less expressive for data modeling purposes than relations, but if I am wrong about that, I definitely would like to be corrected. Thanks for your help. --dawn Received on Sun Jan 11 2004 - 21:06:01 CST