Re: OO's best feature survey results

"Bob Badour" <bbadour_at_golden.net> wrote in message news:<H6KdnQf86rTNUTiiRVn-sQ_at_golden.net>...
> "Topmind" <topmind_at_technologist.com> wrote in message
> news:4e705869.0311021410.7dc4737b_at_posting.google.com...
> > >
> > > > Oracle added,
> > > > what's it called, that parent-of operator, to address the BOM issue,
> > > > other extensions have been added to address time-series temporal data,
> > > > full support for temporal and spatial datatypes have been proposed
> > > > many times.
> > >
> > > They are extensions to the languages, but not to The Relational Model.
> > > The RM allows complex types, interval types, recursive operators,
> > > transitive closure, etc.
> > >
> >
> > Allowing and being "part of" are two different things. For example,
> > JOIN may require a way to compare columns from two different
> > tables for equality. However, it does not define *how*
> > equality is derived. A particular "type" may have some
> > goofy test for equality, but relational does not care.
> >
> > I think all that it demands is that operators return
> > Boolean types or Boolean "answers" so that it can match or
> > filter rows and columns. What those operators operate
> > on is not directly part of relational. Traditionally
> > we have used numbers, strings, and dates, but it is not
> > limited to those. (Everything else can probably be derived
> > from just numbers and strings, but that is another debate.)
> >
> > In short, relational only requires that operators return
> > "yes" or "no". Beyond that, it does not give a fudge what
> > they do as long as they don't change data for non-updating
> > queries.
> >
> > Correct me if I am wrong.
>
> Operations can return values of any type. The only type required by the
> relational model is boolean, but that does not mean the relational model
> requires all operations to return booleans.
>
> Concatenation, for instance, returns a character string.

But concatenation is there for our convenience. It is not directly part of relational theory or the "standard" relational operations. A relational language can still be a relational language without having concatenation operations. It is just less useful to a degree.

-T- Received on Mon Nov 03 2003 - 10:27:00 CET