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

Daniel Poon wrote:

>
> Im jumping in on this thread, because there has always something bothering
> me about relational algebra that I want to get an answer to.

        Perhaps you should ask the people at http://dbdebunk.com./ -- there you can contact the actual gurus that work with relational algebra, namely Chris J Date, Hugh Darwen, Fabian Pascal, and McGoveran.

> Ive often heard that rdbms are based on relational algebra, a branch of

        They would be if they were really relational. SQL92 came close, but it was never implemented; SQL99 is a failure, and probably will never be implemented, thanks...

        In fact the only "pure" relational systems were never implemented (Tutorial D), or are theoretical constructs unimplementable in nowadays computing (A Algebra), or are discontinued (QUEL, BS12).

> mathematics. When I studdied mathematics, a long time ago I admit, I never
> encountered relational algebra. The nearest thing I can hazily remember are
> 'relations', which are what you guys would call binary tuples. The algebra
> we used was quite different than the one put about by the rdbms guys.

        That's because relational theory was defined by EF "Ted" Codd... and is restricted to database systems.

> So where can I learn about 'relational algegra'. Does it really exist?

        Your best bet would be Codd's books (out-of-print, hard to find) and Chris J Date's.

> When applying relational algebra to computing, is it a fair assumption to
> say that it is a value based system? Mathematics always seemed more like an
> identity based system to me.

        This part is too hight for me!

-- 
  _
/ \ Leandro Guimarães Faria Corsetti Dutra           +55 (11) 246 96 07
\ / http://homepage.mac.com./leandrod/     BRASIL    +55 (43) 322 89 71
  X  http://tutoriald.sourceforge.net./     mailto:lgcdutra_at_terra.com.br
/ \ Campanha fita ASCII, contra correio HTML    mailto:leandrod_at_mac.com