None the less, by their own admission, there are no pure Relational Model DBMs available, and so my judgment is based upon my experience of those things that do exist. It could not be otherwise. I tend to be extremely suspicious and slightly dismissive of "theoretically pure" arguments and propaganda in general. Until I, as a run-of-the-mill coder am given the opportunity to use a practical implementation of such theories, they are nothing more than that, in the practical sense.

That's a bizarre attitude. So you have something against theoretical physics? There's nothing wrong with theory. It's useful. If the theory has yet to be implemented, that's not necessarily a condemnation of the theory.

However, a large number of very clever people have put the best part of 30 years getting RDMBSs to where they currently are. Whilst some of the marketing decisions taken may have been done on the basis of commercial greed and/or in an absence of a full understanding of the pure Relational Model, not all those that worked on all the current implementations will have been totally ignorant of, nor blind to the theoretical goals.

Actually, they've spent 30 years on developing SQL DBMSs. Unfortunately, for whatever reason, SQL became the standard way back when (in the 70s), presumably because it's "simple". And since, in comparison to what came before it (network & hierarchal DBMSs), SQL is indeed a huge improvement, it quickly became the dominant player in data management. That strongly discourages the creation of a truly relational DBMS, since it could not be 100% SQL-compatible. Market forces being what they are, the big 5 would rather spend time and money on more sure things, despite the technical problems.

Anyway, I'd strongly suggest reading The Third Manifesto. If you don't want to buy the book, reading most of the articles on Database Debunkings will introduce many of the same ideas.

I should also point out that I think Pascal's tone is terrible. It's too angry and condescending, which turns a lot of people off. Nonetheless, the technical content is excellent. Too bad he doesn't seem to understand the old adage about flies and honey.