Re: some ideas about db rheory

From: vldm10 <>
Date: Tue, 14 Jul 2009 07:48:08 -0700 (PDT)
Message-ID: <>

On Jul 10, 4:34 am, paul c <> wrote:
> vldm10 wrote:
> > On Jul 8, 5:30 am, paul c <> wrote:
> >> I doubt if I would get the drift of the rest of your message no matter
> >> how hard I tried
> > You can try at:
> >
> Thanks, not sure if I had ever noticed those messages before but if I
> had I probably would have discounted them as soon as they suggested that
> dependencies are somehow intrinsic to the question when at most they are
> only a way to enumerate or differentiate cases

If you mean FDs and intrinsic properties then note that FDs are on language level and intrinsic properties are not. Note in my paper (see 3.3.3) that I connect intrinsic properties with universal attributes, m-attributes, entity’s attributes, concepts and extensions of concepts.

>(a misleading way if you
> ask me even though I know Date uses them, maybe that's why he concludes
> certain updates are 'unsafe'.  

Note that C. Date in his book “An introduction to database systems” starts his section about DB design with FDs and in fact, it is about FDs and NFs. But one thing confuse me in this section. He didn’t write what are steps in DB design. It will be good if you can write for this user group what are the first two (or three) steps in the DB design using RM.

>Apart from that the various 'principles'
> that he invokes make me uncomfortable because they suggest that some
> approaches are more 'proper' than others, somehow more 'inherent', when
> in fact and in the first place there is no inherent insert or delete in
>   the bare RM.  How an implementation language defines the assertion and
> retraction of facts is closer to a matter of policy than of principle,
> so I sometimes wish Date would say 'policy of ...', instead of
> 'principle of ...'.  People who want to avoid mysticism need to
> recognize the place of logic in an rdbms, where it starts and where it
> ends.  

Yes, logic is great science, precise and strict. But let me give you two examples, which are on basic level in logic – it is about attributes and truth:

  1. One will tell you that lemon is lemon even if its (attribute) color is green.
  2. In some db application about historical persons, you will put (for example) that B. Mussolini had blue eyes. But he had gone from this world before you was born.

>When they suggest a language that can retract certain facts but
> not assert those same facts, or vice-versa, I think their language
> definitions need some more work, to put it mildly!).

Vladimir Odrljin Received on Tue Jul 14 2009 - 16:48:08 CEST

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