Re: Logical equivalence of simple and complex types under the relational model?

"Dawn M. Wolthuis" <dwolt_at_tincat-group.comREMOVE> wrote in message news:cog95u$4em$1_at_news.netins.net...
> "Rene de Visser" <Rene_de_Visser_at_hotmail.de> wrote in message
> news:cofms4$vr$1_at_news.sap-ag.de...
> > I have read a number of papers that discuss whether complex data types
> > should be allowed under the relational model.
> >
> > What I haven't seen analysed is whether there is actually any logical
> > difference (upto renaming/isomorphism) between the resulting models.
> >
> > It seems to me at first sight that
> >
> > 1) RM with simple types
> > 2) RM with complex types
> >
> > are indistiguishable at the logical level.
> <snip>
> > If this is so why was there in the past debate about whether to allow
> > complex types or not, when it seems in theory (and in at least some
> > languages) it makes no logical difference?
>
> All data can be accounted for either way, but there is typically not a
> mapping between metadata. So, even if there is no logical difference,
there
> is a semantic difference that is significant.
>
What is describe above is a metadata mapping, it effectively maps between two logical models. i.e. I am saying that the two logical models are equivalent up to 'Isomorphism', though I think in this case it is more normal to say 'semantic mapping'? As demonstrated above it is even possible to create a model3 that consistently includes model1 and model2.

i.e. what I am asserting is that there is always a meta data mapping. And that although there is a semantic difference it is effectively one of renaming.

Or do you have a specific counter example?

Rene. Received on Tue Nov 30 2004 - 10:43:57 CET