Re: I think my book may be wrong about cardinality, but I'm not sure

Bruce C. Baker wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:46a90c7e$0$8837$9a566e8b_at_news.aliant.net...
>
>>Bruce C. Baker wrote:
...

>>>
>>>I think I see where you're going with True and False as defined in your 
>>>post, though ...
>>
>>It's not so much where I am going as it is where the relational folks have 
>>already gone. In particular D&D.

Not much to be found about Table_Dee and Table_Dum there. I believe Hugh Darwen coined the terms fifteen or more years ago and wrote about them in one or more articles that CJ Date re-published in his columns and books ("Writings" series). Darwen mentioned somewhere that he didn't "discover" these relations, that one or more people working on PRTV or ISBL did, IIRC, perhaps it was a guy named Stephen Todd. They seem important to me, so I'd be a little curious to know who first came up with them or whether it was one of those notions that occurs to bright groups of people once in a rare while. Again, my memory could well be faulty, but I seem to remember Darwen mentioning that he had brought up tables with no columns or relations with no attributes or something like that to Codd and Codd had dismissed them. I wonder whether his reasons had more to do with practice than theory?

Anyway, if a set can "be" and yet not have members, it certainly seems that a relation with an empty header is possible. And DEE is an obvious identity for join, eg., A <AND> DEE = A. I believe that in TD, DEE is represented as "TRUE". Try and put that "tuple" in your N-dimensional space!

Some of the columns about these tables were published in a magazine called Database Programming and Design, DBPD for short, which is now called "Intelligent Enterprise such and such" or similar oxymoron. Its online archives might still have some of Date's versions of Darwen's papers. I remember when I first saw them and lights started to go off in my head because they were so approachable, like a lot of those old columns, short and sweetly sensible with a minimum of technical lingo. Reading that magazine was an experience somewhere between schizophrenia, psychodelia and maybe Philadelphia because I'd first look at Date's column, accidentally flip a couple of pages and be confronted with one of the several other columnists' mumbo-jumbo. I always figured the publishers had made some mistake, kind of the reverse of Mr. Bean being hired as an art historian.

I hope Bob B will correct anything I've got wrong above. It seems like a month since he's corrected anything of mine but it's been a lifelong (so far) trait of mine that I can't go that long without saying *something* wrong. Perhaps he's losing interest like Fabian P.

p Received on Fri Jul 27 2007 - 03:36:22 CEST