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Home -> Community -> Usenet -> comp.databases.theory -> Re: The wisdom of the object mentors (Was: Searching OO Associations with RDBMS Persistence Models)
Bob Badour has clarified what I meant. RM defines clearly separation
between operators and operation.
erk wrote:
> Bob Badour wrote:
> > I believe Cimode misspoke. The definition of 'operator' as a symbol
> > signifying an operation is a basic definition in computing--all of
> > computing. You can verify that in the ISO standard definitions if you
> > want to.
>
> Is there a link for their computing definitions? Or is it available for
> purchase only? My googling on this isn't turning up what I need.
>
> > > So you're talking about the algebraic definition of a type, like
> > > pop(push(S, x)) = x for a stack?
> >
> > No, he is talking about the definition of a type. An algebra simply
> > restricts the operations to those defined only on the type. Algebras
> > have the desirable property of closure, which is very handy for nesting.
>
> Hmm... I thought algebras were a little more flexible than that. I
> certainly understand the value of closure, but the push operation above
> clearly isn't defined only over the stack domain.
>
> > Thus, while length and substring are operations on strings--being
> > defined using strings and integers--they are not part of either string
> > or integer algebra. Catenation, on the other hand, is part of the string
> > algebra.
>
> OK. So the above isn't truly a stack algebra? And you couldn't write
> the following as part of the string algebra? Does the relational
> algebra truly not involve domains other than relations? It makes
> reference to at least equality in the domains of attributes, doesn't
> it?
>
> - erk
Received on Mon Jun 05 2006 - 13:41:04 CDT