Re: The Fact of relational algebra (was Re: Clean Object Class Design -- What is it?)

From: Leandro Guimarães Faria Corsetti Dutra <leandrod_at_mac.com>
Date: Wed, 03 Oct 2001 22:47:10 -0300
Message-ID: <3BBBBF9E.4090002@mac.com>

Daniel Poon wrote:

> "Leandro Guimarães Faria Corsetti Dutra" <leandrod_at_mac.com> wrote in message
>

>>That's because relational theory was defined by EF "Ted" Codd... and is
>>restricted to database systems.

>
> I seem to remember the rdbms guys redefined 'completeness', to something
> that has no bearing on mathematical compeletness (which I cant remember the

Can you expand on that?

> definition of anymore). I mean, mechanical engineers use applied mathematics
> to underpin their theories, but they don't go an redefine fundamental
> concepts on a whim! So why do computer scientists do that???

They didn't. It's not a redefinition, it's a definition. It's a branch of Mathmatics not because some pure Mathematician said so, but because Codd used Mathmatics to create it, and it is a logical theory using the tools, language and methods of Mathmatics -- but not in the realm of pure traditional Mathmatics.

Now, what other people have done is to bastardize the relational theory, but that's no Codd's fault -- and the tragical result is SQL.

What "fundamental concepts" do you think that relational algebra redefines?

>>>When applying relational algebra to computing, is it a fair assumption

> to

>>>say that it is a value based system? Mathematics always seemed more like

> an

>>>identity based system to me.
>>>
>>This part is too hight for me!

>
> But I think its kind of important. I think you could re-implement relational
> algebra with identity based semantics. I think it would be a lot closer to
> set theory then. Set theory is what people use to 'implement' mathematics
> these days ;-)

Important as it may be, I do not know enough to understand your

question.

Jan Hidders wrote:

 >
 > What do you mean by "based on"? The relational algebra plays a role in
 > query optimization, but that is about it. It helped the introduction of

	No, not at all.  It defines all *logical* structure of an RDBMS and of a

relational database.

 > the relational model because there are some nice links with logic and
 > model theory, but I wouldn't call it fundamental and by itself it is
 > certainly not a branch of mathematics.

	It was created as a branch of Mathmatics, and it is fundamental to RDBMS's use

of the relational model.

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Received on Wed Oct 03 2001 - 20:47:10 CDT