Re: Stored fields ordered left to right

"Bob Badour" <bbadour_at_golden.net> wrote in message news:v6mdnQYXkoaxl3OiRVn-uw_at_golden.net...
> "Marshall Spight" <mspight_at_dnai.com> wrote in message
> news:VBhHb.671183$Tr4.1678668_at_attbi_s03...
> >
> > 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?!?

I was speaking of logically distinguishing attributes. I don't see how the physical level is even relevant here.

> > 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.

Interesting distinction, but not one that I can follow without further information. Do you have a reference for further reading?

> > 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!

Mumble. Operations like union, intersection, difference, are identical either way. Join needs some work, but it's not what I'd call a huge issue.

Marshall Received on Sun Dec 28 2003 - 23:24:09 CET