Re: Relation Schemata vs. Relation Variables
Date: 21 Aug 2006 06:08:20 -0700
Message-ID: <1156165700.829902.184170_at_m73g2000cwd.googlegroups.com>
Marshall wrote:
[...]
> The idea of transition constraints is inherrently non-set-theoretic,
> because it assumes tuple-identity.
How come ? One can easily think about a transition constraint in set terms by extending the original universe with a new attribute value. Then declarative TC specification would be no different from any other integrity constraint specification. That's, by the way, is what Dataphor does with its 'old' and 'new' values.
>Since it is possible to
> model non-tuple-identity scenarios in the RM, there will be
> some scenarios in which transition constraints do not make
> sense.
What exactly do you have in mind when you talk about "some scenarios in which transition constraints do not make sense" ? Received on Mon Aug 21 2006 - 15:08:20 CEST