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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 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?