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

In message <slrncam0cu.9q6.choess_at_force.stwing.upenn.edu>, Chris Hoess <choess_at_stwing.upenn.edu> writes
>In article <PAu0b6GWsqpAFwSz_at_thewolery.demon.co.uk>, Anthony W. Youngman wrote:
>>
>> It's just that I find Newtonian mechanics an excellent analogy. To
>> express it in computerese, both Newtonian Mechanics and Relational
>> Theory are instances of the class Mathematical_Theory. BOTH are
>> mathematically perfect (well, I know Newtonian Mechanics is).
>
>But you're missing an important point, namely, Newtownian mechanics
>incorporates into it distinct physical concepts such as mass, distance, and
>time. Relational theory does not. This is why we can't set up some
>experiment to test "relational theory" as such against the real world and
>see what happens: only by creating a specific schema which links together
>machine-readable definitions of relations and constraints and the semantic
>import of those relations can we try and test relational theory, or any
>other general theory of data modelling, against the real world.

If we can't set up an experiment (even a Gedanken thought experiment), then relational theory is not provable, therefor it is not scientific, therefor it is irrelevant to the real world, therefor why the hell are we using it :-)

As a scientist/engineer type, not a mathematician, I want some experimental proof at least. Unfortunately, all the (anecdotal) evidence I have says that other models work better ...
>
>To put it another way, relational theory is analogous to the equation for a
>Gaussian distribution, f(x) = ae^(-bx^2). Were I to assert that Gaussian
>distributions are useful in describing scientific phenomena, you might ask
>me for a test; and what are f, a, b, and x? And when I tell you that it
>depends on the phenomenon we are trying to describe, and that f, a, b, and x
>can be many different things, you might mistake it to be of no practical
>value, as it makes no verifiable predictions. But if I were to substitute
>for f C, the concentration, for a C0/sqrt(4piDt), for b 1/4Dt, and
>proclaimed x to be distance, I would have made use of a Gaussian
>distribution to describe the process of diffusion, and it could be checked
>experimentally and the predictions of the equation (Fick's Second Law)
>verified. Only by giving a physical interpretation to the variables of the
>Gaussian distribution does it become a scientifically verifiable theory; and
>only by creating a schema which we associate with semantics are we able to
>test the application of the relational model to our problems.

Yup! We have an experiment!
>
>Having established that the relational model is an underlying mathematical
>framework bound to reality by the "glue" of the schemas we create, we're on
>better grounds to discuss the applicability of the model without premature
>calls for "experiment". We know that data in the relational model is
>formulated as logical propositions whose validity is evaluated by
>first-order logic. Hence my tenative suggestion in a post here about a month
>ago for examining alternatives to the relational model: are logical
>propositions the best way to formulate data, and do we need more power than
>first-order logic can bring us (and what trade-offs does that present)?

If we accept that data is an abstract proposition INSIDE relational theory, then I might well agree that logical propositions, first-order logic etc may well be the best way to formulate data. But that implies that data is fundamental to database theory in the same way as mass and energy individually are fundamental to Special Relativity - ie they are NOT - there is a supra-concept called mass-energy, and the transformation between mass and energy is part of the theory and nothing to do with the metaphysical interface to reality ...
>
>(Incidentally, can we agree that while consistency is not sufficient to
>prove the correctness of a data model, it is necessary?)
>
Of course. I'd actually rephrase that. While (internal) consistency may prove the model to be correct (mathematically), we need external consistency to prove the model accurate (here we go - arguing over the meaning of words again :-)

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