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

In message <mvlib01f82t7l1a8vtfdi2u43ako8pboi5_at_4ax.com>, Gene Wirchenko <genew_at_mail.ocis.net> writes
>"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote:
>
>>"Tony" <andrewst_at_onetel.net.uk> wrote in message
>>news:c0e3f26e.0405290915.17c5cb88_at_posting.google.com...
>
>[snip]
>
>>If there is a tight mathematical definition of "data" within relational
>>theory, then that's great, but it is not the commonly used definition, I
>>suspect. It is in the leap from doing relational theory to thinking that
>>the application of such theory is the best approach to storing/retrieving
>>propositions using computers by a business -- that is where there is a
>>rather significant leap of faith. That connection is NOT science, although
>>we could conceivably set up some experiments to collect a bit more
>>information about whether it is better than some other approach. I'm not
>>opposed to faith, but we need to call it what it is. There is mathematical
>>relational theory and then a leap of faith in the use of relational theory
>>for anything.
>
> It is an even bigger leap of faith to operate without a theory
>underlying what you are doing.
>
>>> Now, when someone uses the relational model to build a database
>>> corresponding to some real world thing, say a payroll system, then it
>>> is up to the database designer (not the relational model) to ensure
>>> that what he builds corresponds to the reality he is building it for.
>>
>>And perhaps that person opts out of using (at least all of) relational
>>theory and that's fine, right?
>
> What is the replacing theory? Is it better or worse? How do you
>know? Is the consideration of better/worse a leap of faith? If not,
>why not?
>
I was thinking of replying to Tony, but I think I can answer here.

And no, Tony, Einstein did NOT "build a better model" using the same algebra. What he DID do was realise that Newton's fundamental axioms were wrong. He redefined the metaphysical interface between reality and the model.

And the problem I have is that I cannot see any metaphysical interface between reality and relational theory. This is basically Dawn's point about "is relational theory even the right theory to use?".

As for Gene, I agree we need a theory, and actually, I think relational theory is a great theory. Unfortunately it is a theory about a - call it abstract, call it imaginary, they're the same thing - concept called "data" that does not seem to have any basis in the real world.

So what do I think should replace it? Nothing actually, we can just improve it. BUT IN DOING SO, IT WILL BE TRANSFORMED BEYOND RECOGNITION :-)

Go back to my analogies :-) In hindsight, we just can't understand why the Church couldn't see that Copernicus' theory that the planets orbit the sun didn't make sense. Except that *WE* have got Copernicus' theory wrong. He thought that the planets *circled* the sun. And as a result his theory was just as much as mess (if not more) than that of the Church who said the planets and sun orbited the earth. I think *that* is the current state of database theory.

What we NEED is a "theory of business analysis" - a formal theory that tells analysts how to analyse the real world. And I'm pretty damn confident that you can NOT create a theory that will do a reversible mapping between the real world and relational data.

This theory will then be the equivalent of Kepler and Newton discovering ellipses and calculus, or of Einstein realising that mass and energy were interchangeable. Basically, pretty much ALL of relational theory's axioms are taken as given by the mathematicians, and no thought is given as to whether they actually match the real world.

To give you a simple example, the business analyst analyses an invoice, and you design the database to store the data. Can you then ask the DATABASE to give you the invoice data back? Certainly with current relational databases accessed with SQL, you're relying on either an application programmed OVER the database, or a view which gives you multiple copies of data of which the original only had one.

Yes I know people are likely to say that "SQL is not genuine relational", but you're still relying on a view - even a valid relational one - or an application.

If we can't go - using formal theory - from the database back through the analysis to get back to the real world we started from, then we have no idea if our axioms are correct, and as Dawn says, we have no idea if relational theory is the correct theory to solve real world problems.

And as I said before, it we have no idea if it's the correct theory, why are we using it? Dawn was going on about faith. Do you have faith in business analysts to get the analysis correct, or would you rather have a formal, REVERSIBLE and PROVABLE (or testable, falsifiable, scientific, whatever term you want to use) logical theory to do it for you?

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