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

Daniel,

> Engineers seem to use mathematics to communicate. In computer science they
> seem to use mathematics to create walls. Maybe thats just how it seems at
> the moment. It would be good if everyone had some knowlege of set theory.

One of the distinguishing features of the relational model of data is that it was developed by a single individual, not by a committee or a succession of champions. Another distinguishing feature is that the relational model of data was derived, with a degree of rigor uncommon in computer science, from mathematics itself. The mathematics that provides the rigorous foundation for the relational model of data is an extension of set theory. I have heard this extension consistently referred to as "relational algebra". Relational Algebra was not commonly taught in high schools in decades gone by, and I doubt that it is commonly taught in high schools today.

Still, it would be good if everyone had some knowledge of set theory, as you said. I have taught elementary relational database design and programming to computer professionals, and the hardest thing to get traditionalists to understand is that a query specifies a set of data, perhaps ordered into a stream. For people whose thinking is bound to one-record-at-a-time processing, this is too much to swallow, and they never get beyond trying to beat the query optimizer at its own game. The people who have some knowledge of set theory seem to grasp the fundamentals of relational queries a little quicker, on the average, than those who don't.

Here in the "comp.databases.theory" NG, the focus is a little different than it might be in a "comp.databases.practice" NG, if such an NG existed. For many participants, the topic of interest is not how existing DBMS products work, but how they ought to work. That may explain some of the other responses you are getting.

Hope this helps.

--
Regards,
    David Cressey
    www.dcressey.com