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Re: [xml-dev] Caught napping!
Date: Fri, 09 Nov 2001 13:12:35 -0800
From: PaulT <email@example.com>
I can *not* explain why SQL is a poor shadow
or the true RM ( and I doubt that there is many
people, who can ).
I don't know what Fabian Pascal is bothered by, but you might want to
look up some of the old Ingres papers, probably authored or
co-authored by Michael Stonebraker. Ingres had a language called
QUEL, and the Berkeley Ingres guys were pushing QUEL as a competitor
to SQL (then known, I think, as SEQUEL) at the time. I seem to recall
that QUEL proponents liked the fact that QUEL was very closely
modelled on relational calculus, whereas they felt that SQL was a
hybrid of relational calculus and relational algebra, and therefore
impure in some way or other. It's been many, many years since I read
these papers and I might have the story wrong.
I'd love to see a link to that mathematical underpinning
on his website ( www.jclark.com ) or on w3c website.
Personally I think this "mathematical underpinning" business is often
invoked with a mystical aura, lacking a good explanation of what the
benefit of said underpinning is. I use Microsoft Word and Emacs every
day, and they don't have any mathematical underpinning, and somehow it
never seems to bother me. What illness is XML suffering from that
somehow would be healed by a "mathematical underpinning"?
If you want to read a really good book on data modelling, I recommend
"Data And Reality: Basic Assumptions in Data Processing Reconsidered"
by William Kent. This is more about philosophical underpinning than
mathematical underpinning, and it shows just how deep some of the
problems are, including plenty of interesting issues that aren't
solved by the relational model and aren't going to be solved by any
alternative that is a model in the sense that the relational model is
a model. Representing reality as data is hard.
And the author is not ignorant of relational theory. At the time Kent
wrote this book, in 1978, his affiliation was "IBM, San Jose", i.e. he
was right in there with the relational guys, and his preface thanks
both Codd and Date among people who "took the time to comment on (and
often contribute to) this manuscript".