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

In article <PAu0b6GWsqpAFwSz_at_thewolery.demon.co.uk>, Anthony W. Youngman wrote:

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*> It's just that I find Newtonian mechanics an excellent analogy. To
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*> express it in computerese, both Newtonian Mechanics and Relational
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> 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.

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.

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)?

(Incidentally, can we agree that while consistency is not sufficient to
prove the correctness of a data model, it is necessary?)

--
Chris Hoess

Received on Wed May 19 2004 - 08:41:35 CEST
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