Re: Relations contain Objects

"JRStern" <JXSternChangeX2R_at_gte.net> wrote in message news:3d09f498.595906_at_news.verizon.net...
> >Tuples have no operations and visible internal structure. I suppose they
are
> >impure classes. Most people like classes to have behaviour and no visible
> >internal structure, though.
>
> So why isn't tuple a generic class on its own?

Tuple is a generic type, and an RDBMS must have a tuple type generator.

> >> I dunno that an n-ary type is a postulate, ... or, wait, maybe you're
> >> onto something there. Would you like to say more about it? Do you
> >> have any reference to a book that treats things that way?
> >
> >Any book on first order predicate logic.
>
> That's swell, but when we talk database, are we talking predicate
> logic or set theory?

They are equivalent.

> Are we talking postulates or facts (axioms)?

Postulates is synonymous with axioms.

> Don't heterogenous and typed entities take us outside of either basic
> mathematical model?

No, I don't believe it does. Why would you think so?

> >> If you have an entity which is a relational variable, then I still
> >> have an issue with whether its value is the tuples, or the
> >> specification of those tuples, or both. I'm uncomfortable with
> >> "both".
> >
> >It's value is its value. A value carries its type with it. For instance,
the
> >value 3 is an integer.
>
> Not good enough. When the "value" is complex, you have a problem of
> by-value or by-reference (and in some contexts, by-name).

In the relational model, all external references are established by relations whether stated or derived. One can say that update operations probably are implented with by-reference parameters, but this is not required by the logical model.

> If I have an integer 3 and a real 3, are they the same type?
> Nope. Lots of issues hereabouts.

Yes, they are. They are in the inheritance model prescribed by _The Third Manifesto_. Integer is a subtype of real. When a variable of "declared type" Real contains the value 3, it contains a value with "most specific type" Integer (or Whole or Natural if these are sub-types of Integer in the type system.)

I have no issues with it at all. I think it works great. Received on Fri Jun 14 2002 - 22:22:22 CEST