Re: In an RDBMS, what does "Data" mean?

In message <DEv3K2FwTOxAFwzu_at_thewolery.demon.co.uk>, Anthony W. Youngman <wol_at_thewolery.demon.co.uk> writes
>In message <5k2xc.6205$4b2.1710_at_newssvr32.news.prodigy.com>, Eric Kaun
><ekaun_at_yahoo.com> writes
>>> A data model that can do this has many advantages.
>>
>>That can do what - model arbitrary data in its "natural form", whatever that
>>means? I agree. If you show that to me, I'll use it.
>
>And there we have our problem.
>
>Yep, I can see where you're coming from, in practical terms. But can't
>you see where we're coming from? My problem, as I see it, is that
>'arbitrary data in its "natural form" ' is NOT amenable to easy
>coercion into "relational data".
>
>From that, it follows that relational databases are the wrong tool to
>model natural data with.
>
>However, as I said, I do feel that it's like the circle/ellipse problem
>that Copernicus had. IF people are prepared to *look* at real data in
>its "natural form" and develop a model that really addresses that,
>while it will make one hell of a mess of current relational theory,
>combining a "natural form data" model with the relational model will
>yield a very powerful database theory.
>
>After all, isn't that exactly what I do when I insist on normalising
>all my data within Pick FILEs? And I really don't see the problems you
>do, even if the line-items come from multiple warehouses etc etc. If
>the relational analyst didn't foresee that, you're going to end up in
>an equally big mess (experience says "even bigger" mess) than a Pickie,
>if both are faced with the same analysis failure.
>
Following up to myself, a line item on an order is different to a line item on a delivery note is different to a line item on an invoice. I know analysts screw up and get it wrong, but I'll draw an almost identical analogy :-)

If your customer's warehouse moves, you do NOT want changing the warehouse address to change the delivery address on all your old invoices... so while your line item on the invoice may point to the line item on the delivery note, it MUST NOT be the same "object". Because things change. After all, in the transition from order to delivery note, it's quite possible for you to substitute an equivalent. And you can't even guarantee that the invoice line will always be identical to the delivery note rather than the order - because certainly under UK law, if the supplier substitutes on their own initiative they are obliged to bill the cheaper item, not the one that was actually supplied ...

Cheers,
Wol

-- 
Anthony W. Youngman - wol at thewolery dot demon dot co dot uk
HEX wondered how much he should tell the Wizards. He felt it would not be a
good idea to burden them with too much input. Hex always thought of his reports
as Lies-to-People.
The Science of Discworld : (c) Terry Pratchett 1999