--- Bill Walton <[EMAIL PROTECTED]> wrote:

> 
> Exactly.  Without the intervening layer introduced by the Relational
> Model,
> a search is intimately and inextricably bound to the underlying
> structure of
> the data to be searched.  Change the structure of the data and you
> have to
> change the programs that access it.  That is the problem, along with
> a host
> of related ones, that Codd set out to solve.  The Relational Model
> solved
> that problem and did so in a mathematically provable way.  The
> "mathematically provable" part is what you found so enlightening on
> the
> Wikipedia ;-)
> 
> Best regards,
> Bill
> 
> Kevin
> 

I like to think of the relational model as playing a role in database
theory analogous to that of Turing machines or lambda calculus in
language theory. Turing machines may be particularly efficient ways to
implement programming languages (or computers), but they are formal
mathematical models we can reason about. The same goes for lambda
calculus, of course, but the first functional languages were about 100
times slower than Fortran or assembly language. That's changed
considerably, and today the best compilers for functional languages
achieve about 70% of the performance of C. Similarly, relational
databases often get a bad rap in the MUMPS community because they are
perceived as inherently slow. But that is a category error: an
*implementation* can be slow, but a logical mode is neither fast nor
slow, it is a formal framework for *reasoning* about databases and
database queries. I'll leave it to others to argue about the state of
the art in design of (concrete) relational database systems, but the
relational model is a mathematical framework like a Turing machine. It
should be thought of as a theoretical tool.

===
Gregory Woodhouse  <[EMAIL PROTECTED]>

"It is foolish to answer a question that
you do not understand."
--G. Polya ("How to Solve It")


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