Re: Why relational algebra is algebra

Mikito Harakiri wrote:
> 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!

Well you *can* define the restrication that way but you don't have to. If you only allow the propositions 'column1 = column2' and 'column = constant' your algebra will have the same expressive power.

> Therefore, relational agebra doesn't seem to be self-contained: it can't
> possibly be axiomatized without bringing in propositional logic at least.

What is the purpose of your axiomatization? How complete do you want your axiomatization to be?

-- 
  Jan Hidders