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Re: Logical equivalence of simple and complex types under the relational model?

From: Rene de Visser <Rene_de_Visser_at_hotmail.de>
Date: Thu, 2 Dec 2004 13:48:01 +0100
Message-ID: <con2u2$l3a$1@news.sap-ag.de>


"Costin Cozianu" <c_cozianu_at_hotmail.com> wrote in message news:3176hhF37fv4iU1_at_individual.net...
> Rene de Visser wrote:
>
> You are not forced into doing that, but it has been proven the sensible
> solution by some 50 years of experience with programming languages,
> logics and other formal language applications.

I have spent most of my life (so far) programming in imperative, functional and OO langauges.
At the moment I am getting used to programming in a declarative relational language operating inside of an active database. It has some interesting 'unification' between types, functions and relations which seems to change the cost / benefits of doing things the way you normally would.

I agree with your statement above, but I think even the best programming languages that we have now are only about 10% of what an ideal language would be (I think that a clean mix of Glasgow Haskell (including extensions), peristant, relational and declarative languages is possible, just very difficult).

And that in such a programming language, where you are mostly operating at the specification level will have different good programming practices than the last 50 years of experience (which I think is very hetrogenous and language type dependant).
>
>
> > [Aside: the address_id is not a pet. It can look after itself, or the
DBMS
> > can look after it]
> >
> >
>
> So what exactly would an address_id be ? A reference to a particular
> address stoired in the central global_addresses ?
>
> >>There's no need to have "identity" for values. Values are
> >>self-identifying. If you have the number 3 you don't need an 3_ID for it
> >>to identify. So if you have the address ((zip 1234) (street "X no 4")
> >>(country "USA")) that's your value right there, just like the value 3.
> >
> >
> > Theres no need to have identity for complex type instances. But then I
would
> > claim that you need equivalence classes, and that these are effectively
the
> > same.
> >

You are correct that there is no need to have identity for IMMUTABLE values. However from the way you had spoken about your address object, I had taken, that it was a mutable object.
>
> >
>
> It depends on what you want to include in RM. If you want to include
> strictly relational algebra for theoretic explorations, than they are
> for all intents and purposes indistinguishable, because even the
> unnesting operators can be defined with standard operators against their
> domains.

Yes I realised this later, than the decomposition can be done with the standard operators using the correct relations.

Many thanks for your replies. I have to do some reading up, and experimentation with these things. I will also be away for a month and so probably won't be able to reply sensibly to all your points in the next two months.

Rene. Received on Thu Dec 02 2004 - 06:48:01 CST

Original text of this message

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