Why relational algebra is algebra

From: Mikito Harakiri <nospam_at_newsranger.com>
Date: Thu, 12 Jul 2001 19:15:26 GMT
Message-ID: <hHm37.16997$Kf3.220914@www.newsranger.com>

I'm looking into the 'Restrict' operation in Relational algebra (called 'Selection' at
http://www.cis.ohio-state.edu/~gurari/course/cis670/cis670Ch4.html) and don't understand why it is an algebra. 'Restrict' definition contains a propositional formula inside, so that calculus crept into the back door! Now, we can also trade propositional formulas inside 'Restrict' into set operations like this:

restrict(EMP, dept=10 or dept=20)

union( restrict(EMP, dept=10), restrict(EMP, dept=20) )

Therefore, relational agebra doesn't seem to be self-contained: it can't possibly be axiomatized without bringing in propositional logic at least. Am I missing something? Received on Thu Jul 12 2001 - 14:15:26 CDT