Re: Principle of Orthogonal Design
Date: Mon, 28 Jan 2008 02:58:56 -0800 (PST)
On 28 jan, 02:12, mAsterdam <mAster..._at_vrijdag.org> wrote:
> Jan Hidders wrote:
> > mAsterdam wrote something very much like:
> >> Pragmatical redefinitions must be temporary and tracked.
> > Sure, we agree on that.
> Wether the relation between heading and tuples goes
> via names or ordering is relevant or not.
> If it is not I want it out of scope.
I don't think that it is possible to get it out of scope. If you think it is, then by all means provide an equivalent and complete definition where it is. I'm also not sure what your problem exactly is. We have a definition that works for the named perspective, which is arguably the most appropriate for the relational model anyway, so can we now please, please, please, pretty please, move on with the discussion?
> >> DEFINITION: Two relations R and S are said to have dependency-induced
> >> overlap if there is a dependency that requires that sometimes some
> >> tuples(1) of R are also in S.
> >> (1) for some definition of tuples that allows restricted
> >> reshuffling of its values. To do.
> > The only way to achieve (1) so that it also takes all normal inclusion
> > dependencies into account is to define tuples as something equivalent
> > to bags of values.
> Nice, a third alternative way to state the same relation.
> How can this be relevant?
> > Such an operation on its internal organs is going
> > to change the relational model beyond recognition.
> This is hardly surprising when part of the (database local)
> definition of relation is under discussion. More specifically:
> How do tuples conform to relation headers?
> > I'm going to
> > strongly insist that we stick to the classical definitions of the
> > named perspective and state in the definition that we are talking
> > about inclusion up to relabeling:
> > DEFINITION: Two relations R and S are said to have dependency-induced
> > overlap if there is a dependency that requires that sometimes some
> > tuples of R are also in S after renaming the attribute names.
> Two glossary todo items: [Trivial](new) and [Type].
> The s/meaning overlap/dependency induced overlap/
> did help to clarify.
> This time 'type' is the label on a jar containing something else.
> Do you have a suggestion for
> in PoOD related discussions ?
Yes, don't. :-) IMNSHO that part of the POOD discussion clearly doesn't make sense and at best leads only to a crippled version of the relational model. But if you insist and want a name for that kind of thing then I can tell that suspect (but might be wrong because it's not really well defined) that the thing your are talking about is often called a "named type", and if you want to emphasize that you are talking about the other kind the term "anonymous type" is often used.
- Jan Hidders