Re: Date's First Great Blunder
Date: Tue, 20 Apr 2004 18:59:57 -0300
Message-ID: <pan.2004.04.20.21.59.42.601465_at_dutra.fastmail.fm>
Em Mon, 19 Apr 2004 22:40:56 -0700, Neo escreveu:
> You can't prove a system to be correct by using
> the system itself as a reference. You must use reality as a reference.
A very interesting philosophycal issue.
A system in itself isn't correct, but consistent. External consistency is what we usually call correctness. But a self-inconsistent or ill-defined system by definition can't be correct in a rational world.
Now taking databases and their general data models as systems, SQL is inconsistent, as are the so-called OO, XML, network and hierarchical models, which are actually fuzzy generalizations stemming from implementations of programming methods, not data models. One could perhaps define a graph model, but it hasn't been done and would certainly result much less powerful and more complex than the relational model.
> What exactly is RDM modelling
> in the real world when it incurrs NULLs?
NULLs aren't part of the RDM. Codd did include them, but they are not necessary and increase complexity too much. Special values in the relevant domains do the trick quite nicely.
-- Leandro Guimarães Faria Corsetti Dutra +55 (11) 5685 2219 Av Sgto Geraldo Santana, 1100 6/71 +55 (11) 5686 9607 04.674-000 São Paulo, SP BRASIL http://br.geocities.com./lgcdutra/Received on Tue Apr 20 2004 - 23:59:57 CEST