Re: A different definition of MINUS, Part 3

Cimode wrote:
....
There are a lot of problems related to deriving a language definition
directly from traditional algebra, one of them being determining a
semantics that maps to RL traditional formalism in an exhaustive
fashion, while remaining effective to be expressed semantically by a
programmer. Since defining a language does not answer the same
problem than establishing a theorem, it is difficult for me to imagine
they could both be similar solutions.
...

I think those are profound observations. I imagine it is easy for a designer to fall into the trap of designing a language for the algebra instead of designing a language for the purposes in mind. For example, Codd wrote very little about his calculus and algebra per se compared to everything else. From the get-go, he had various operators called JOIN. For all I know, he did not think his join was defined by the TD join and so not by the A-algebra A <AND> B definition. We all must die and of course I don't like the idea but in his case we all have an especial reason to be sorry he is dead. I met him once, just as his book was coming out, but I was so completely ignorant about the relationship of the calculus to the algebra that I didn't think to ask him any questions about that. Although I knew a bit of the calculus, I hadn't made the algebra connection and the standard advice I gave to journeymen Cobol programmers and such was very crude, having to do with I then called 'regular' sentences. Strangely enough, people whose native languages wasn't English seemed to me to do better with this advice than the native speakers.
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