Re: The Practical Benefits of the Relational Model

Costin,

> But since you are the one who claimed in this thread that OO has pretty much
> all the bad qualities and the relational model (or to say more acurately:
> the proposal of Date & Darwen for "future directions of data and database
> management systems") comes and cure them all, including the "type
> inheritance" , I'll ask you if you did your homework and read the references
> I gave you.
>
> Having read those references how do you see the initial statements that
> you've made?
> Are you aware now of the difference between subtyping and inheritance, and
> what is the practical benefit of separating subtyping from inheritance?
>
> I ask you these questions, because I don't want top engage with you in a
> long discussion where I have to restate all the things that you ought to
> have read, should you have tried to properly *learn* about the domain of
> which you are making such bold claims.

I have read the paper Type Systems by Luca Cardelli, and I can only say we must agree to disagree.

Firstly, just because a given definition does not include a bunch of symbols (that mean different things everywhere they appear, by the way) does not make that definition any less formal. Formal is not equal to symbolic. Prose can be just as formal as symbols, and more readable!

Secondly, these 'formal systems' to which you are referring are exactly the opposite of what Date and Darwen have done in The Third Manifesto (indeed they state as much in the book itself). The type inheritance :P model presented in TTM is a logical model describing the expected behavior of a system. The 'formal type systems' described by Cardelli are an attempt to extract a formal model from existing implementations. As a result they contain 'formalizations' for all kinds of constructs which have no counterpart in the real world. It strikes me as pretty unlikely that Date & Darwen were ignorant of this body of research, rather I believe they made a careful study of it, and determined that it had taken a completely different approach. As such it was discarded as inapplicable to the problem they were trying to solve.

So no, the type inheritance model presented in TTM is not a 'Type System' by Cardelli's definition, but I believe deliberately so. I'm sure you will obtain much better responses to these types of questions from Date & Darwen themselves. As for our part, we remain unconvinced that the Type Systems you reference provide a good foundation for building a _logical_ model which matches the real world as closely as possible.

Regards
Bryn Rhodes
Alphora Received on Tue Oct 01 2002 - 19:35:02 CEST