Re: object algebra

neo55592_at_hotmail.com (Neo) wrote in message news:<4b45d3ad.0402241444.2335842f_at_posting.google.com>...
> > > > > Under RDM, closure requires meeting rather strict criteria (chapter 6)
> > > > > in comparision to criteria for closure in TDM.
> >
> > The point is: if your result has an arbitrary shape, because your inputs
> > have arbitrary shape, then your answer is shapeless and meaningless.
>
> TDM allows arbitrary shape inputs to produce arbitrary shape outputs.
> Whether it has meaning or not is application specific.
>
> > execute a query and "join" A to B using the ASCII value of the 3rd character
> > of A.x and the square root of B.y if you really want to - you just can't
> > expect it to make any sense. But at least in that case the answer would be
> > consistent with your predicates and data, unlike a "shapless" result set.
>
> I am concerned with the validity of a join or operation. That is
> application specific. I am concerned with the degree of closure that
> the model provides over any concievable operation. As you pointed out,
> in RDM operations have some "shape" requirements. TDM doesn't.

One of the great strengths of the relational model is that *nothing* is application-specific. The data stands on its own. Applications come and go, and get rewritten in the current tools in vogue, but the data is still needed. Received on Wed Feb 25 2004 - 11:54:13 CET