Re: Guessing?
Date: Sun, 01 Jun 2008 00:42:00 GMT
Message-ID: <sfm0k.179265$rd2.156266_at_pd7urf3no>
[Quoted] Brian Selzer wrote:
...
>> That seems to be part of an argument about something else. >>
>
> Indeed. It is not about unions but rather about strong orthogonality, which
> is what I thought we were discussing.
[Quoted] Maybe you did, but the Codd quote in the OP was about what some see as one of the the view updating problems, which is about whether a dbms can perform certain updates in a manner that is consistent with how it replaces base relations (I'd say replace is a far more precise word in this case). POOD, which is a proposed solution, was mentioned, but it carries other baggage having to do with human preferences and, as usual, gets attacked on grounds that don't have to do with the original problem.
When the relations in a union view expression are union-compatible (so-called), I wish somebody could show me how any disjunction is involed in the tuples of the union view. Many people say that the predicate must be disjunctive, but I'd say that the machinery of the RM has completely discounted that. Received on Sun Jun 01 2008 - 02:42:00 CEST