Re: Relations contain Objects

"JRStern" <JXSternChangeX2R_at_gte.net> wrote in message news:3d0926bd.30867394_at_news.verizon.net...
> On 12 Jun 2002 13:33:19 -0700, jraustin1_at_hotmail.com (James) wrote:
> >> > What does an OODB-model lack
> >> > that prevents it from being as expressive as a RDB-model?
> >>
> >> Relations.
> >
> >I think I now understand, and agree, the fundamental basis of
> >databases is the 'fundamental concept' described by a relation.
> >According to relational terminology: a relation is a set of related
> >things.
>
> I don't know if "relation" is supposed to mean the semantic function
> that groups fields, or a particular set of values that fulfills the
> function. That is, I forget if it's supposed to mean a table or a
> row.

A relation, in this case, is a generic type with generic operations consisting of header with a set of N named, typed attributes and a set of N-dimensional tuples where a value in each dimension of each tuple corresponds to one of the named, typed attributes.

> But the term "object" is used loosely to mean class or instance, so
> "object" doesn't map exactly to anything.

What does class or instance mean?
ie:
How does a class differ from a type?
How does an instance differ from a variable?

> IOW:
>
> table == class
> row == instance

I find the above comparison lacking at a number of levels. I would propose different ones that I think are much more useful.

Since the values in relations can have arbitrary complexity:

type == class
value == object value
tuple (row) == set of associated object values--equally an N-ary postulate relation == set of N-ary object value postulates relation variable (table) == set of N-ary object *variable* postulates insert into relation variable == instantiate instantiate == specify a tuple value Received on Fri Jun 14 2002 - 02:53:20 CEST