Re: Dreaming About Redesigning SQL

Paul G. Brown wrote:
>
> Erm . .
>
> What's 'physical' about this?
>
> RELATION Dept ( Id Dept_Id KEY, Name String ); [....]

Absolutely nothing, of course, and just about any expert on database theory (people who had several publications on PODS, ICDT, et cetera) that I talked to about this agrees with you on this. In fact, I also talked to some logicians (you know, people who actually know about what is logical and what is not, :-)) about this question, and their answer was that from their point of view it was in fact the String-part that was less logical. This is not easy to explain in a few sentences but if you are interested in the links between logic and the relational model I can recommend you:

   Jan Van den Bussche: Applications of Alfred Tarski's Ideas in    Database Theory. CSL 2001: 20-37

It's on-line at:

   http://citeseer.nj.nec.com/vandenbussche01applications.html

Especially important is the reference

   [59] A. Tarski, "What are logical notions?", History and Philosophy

         of Logic, 7:143-154, 1986, Edited by J. Corcoran.

but unfortunately I couldn't find that on-line. To get an idea read the definitions at the end of page 2 and beginning of page 3 in the paper by Van den Bussche. It's not easy stuff if you're not used to it, but I hope you will understand that what it says there is that logical notions treat the atomic values as *abstract* values, which is what references, object identifiers, logical pointers or whatever you want to call them, actually are. And Alfred Tarski, who may be considered as one of the founders of modern logic, consideres this to be such a fundamental property of logical notions that he in fact uses it as the very definition of what a logical notion is.

So am I arguing that we should only use abstract values in the columns of our relations? Certainly not. What Tarski presents here is a simplified model that he uses to understand certain properties of logical systems. But what this does tell you is that from a logical point of view there is no problem with abstract values and in some sense they can even be regarded as more fundamental than concrete values.

• Jan Hidders