Do values have constraints?

"Bob Badour" <bbadour_at_golden.net> wrote in message news:KmP5b.506$ad6.48870536_at_mantis.golden.net... [snip]
> > But as I said, I don't believe that type inheritance needs to be defined
> > separately for relations. See IM Prescription 25: Tuple/relation Variables
> > with Inheritance for more details.
> >
> > Constaints are not part of the type specficition of relations and tuples.
>
> Obviously, I think they are regardless of any artificial distinction. Do you
> have a reason for thinking the distinction is necessary?

What about foreign key and other database constraints.

if attribute F in relvar A(F INTEGER) is a foreign key from relvar B(F INTEGER), what is the type of relvar A? How do we reference relvar B in the type definition of A? Should type definitions be dependent on the existence of variables? Do the valid values of the type of relvar A change depending on the contents of relvar B?

Regards
Paul Vernon
Business Intelligence, IBM Global Services Received on Fri Sep 05 2003 - 16:46:53 CEST