Re: Stored fields ordered left to right

"Marshall Spight" <mspight_at_dnai.com> wrote in message news:VBhHb.671183$Tr4.1678668_at_attbi_s03...
> "Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
news:bsira5$jlt$1_at_news.netins.net...
> >
> > I've been puzzled by this for quite a while, just figuring that
relational
> > theorists have this wrong. But the writings seem so sure of this. I had
> > thought that the relations in relational database theory were
mathematical
> > relations, but I am beginning to think that might not be the case. My
> > masters in mathematics was quite some time ago, so I hauled out some
books
> > and googled a bit and everything I find that is mathematics, rather than
> > database theory, indicates what I thought about relations -- a relation
is a
> > set of ordered tuples -- right? What am I missing here?
>
> I'll give you my perspective, but I don't know how much it'll help.
>
> The question is, how does one distinguish the attributes in the relation?
> There are two choices: numerically/positionally, or by name. That is,
> one either has a mapping from 1, 2, ... n to attribute, or one has
> a mapping from name1, name2, ... namen to attribute. To me, it's
> not all that great a difference. It's just a question of what the
application
> is.

Physical dependence vs. physical independence is not that big a difference?!?

> If one is writing a page of equations, the convenience of using
> positional identification is high.

You are confusing an external physical representation with a logical representation.

> It doesn't affect the semantics of relations or relational operators;
> it just affects how attributes are identified.

Huh? Of course it affects the semantics if positional ordering has meaning! Received on Sat Dec 27 2003 - 23:39:19 CET