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

"Tom Hester" <thester_at_metadata.com> wrote in message news:f2f74$41abb8de$45033832$19131_at_msgid.meganewsservers.com...
> Rene de Visser wrote:
> > 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.
> languages) it makes no logical difference?
> >
> > Rene.
> >
> >
> >
> If you mean literally a logical difference, then there is. The easiest
> way of thinking of logic and databases is to think of the data model as
> an interpretation of a language.
I have not seen this interpretation of RM. Do you have a reference? I aways think of RM as tuples over well formed logical expressions, and then consider the logical system (in the formal sense) generated.

> If the model is composed only of
> simple types then the language is first order function free--the kind of
What do you mean by first order function free? Sorry I don't know the term, but I see google does. I will look it up some time.

Does it really mean 'first order' functions, as in a lambda calculus over relations?

> logic that we all learned as undergraduates. If the model allows
> complex types then the language is no longer function free--it is more

You mean again first order function free?

> complex, allowing functions that define the abstract types.

This would be by definition any way? And the question is still the same. Is allowing functions to define abstract types different than allowing relations to define abstract types? I would think that as functions are a special case of relations, that this must be true. Though if you mean first order functions, then this would only be true in a system allowing first order relations?

Rene. Received on Tue Nov 30 2004 - 10:54:52 CET