Re: Multiple-Attribute Keys and 1NF

On Aug 30, 1:42 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> JOG wrote:
> >>Write a predicate for the relation schema that when extentially quantified
> >>and extended yields a set of atomic formulae that implies all three of the
> >>propositions above. I think you'll find that the colour-code concept is in
> >>that predicate.
>
> > I agree. I hold little stock with set based values so in RM I would go
> > for the addition of colour-code foreign key.
>
> > But what if we weren't tied to a traditional relational schema and
> > tweaked the system so it could allow propositions with more than one
> > role of the same name without decomposing them. As Jan pointed out
> > 'tuples' are no longer functions - they would be unrestricted binary
> > relations (subsets of attribute x values). We could produce a
> > comparatively simpler and less cluttered schema, predicate in a very
> > similar manner as before, and with a few simple alterations could have
> > an equally effective WHERE mechanism. My concern however would be the
> > consequences to JOIN.
>
> What would you offer in place of the RM's logical identity.

Nothing. I am utterly convinced by Date et al's arguments in favour of logical identity. (Why would I need to replace it?) I just wanna model propositions, and they are always identified by their contents. Received on Thu Aug 30 2007 - 13:34:34 CEST