Re: Relations contain Objects

> Silly, you already know that objects equals domains.

An object isn't equivalent to the domain or range. An object is equivalent to an element in either domain or range.

> > > > 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.
>
> Unfortunately, that does not resemble a relational definition of the term.

Although my definition was rather simple it does state the essense of what a relation is: a set of related things.

> Specifically, a relation has a header consisting of a set of N named, typed
> attributes and a body consisting of a set of N-dimensional tuples with a
> value corresponding to each of the named, typed attributes.

Let N = 1

Header: Person

Type:     (text)
          John    {A tuple with the value "John"}
          Mary    {A tuple with the value "John"}

Did I interpret correctly?
Yes, I agree this is an example of a relation, but the below is a more generic manner.

Let Range = {Person}
Let Domain = {John, Mary}
The mapping between Domain and Range is a function which always return Person for any element in the Domain.

Although each element has a type, there is no need to consider it at the logical level. Is there?

> They are the same as mathematical relations.
> Each of the values in every tuple is an object in an OO sense.

Although a tuple has a type, is there is no need to consider it at the logical level? At the physical level, an object has data. The object represent the tuple, the tuple might be a feeling. The object represent the feeling. The object's data simply stores a computer's representation of that feeling.
(www.xdb1.com/Data.asp)

> One can think of a relation as a set of truth statements about N objects of
> arbitrary complexity.

Yes, it does state the essense of what a relation is.

Note: I have updated my definition of an object in thread titled "OOPs! Object is the foundation of a Relation" Received on Fri Jun 14 2002 - 03:35:31 CEST