Re: some ideas about db rheory
Date: Tue, 14 Jul 2009 07:48:08 -0700 (PDT)
Message-ID: <c2b30e0a-e14f-45c9-898f-1e63fddf20dc_at_l31g2000vbp.googlegroups.com>
On Jul 10, 4:34 am, paul c <toledobythe..._at_oohay.ac> wrote:
> vldm10 wrote:
> > On Jul 8, 5:30 am, paul c <toledobythe..._at_oohay.ac> 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:
> >http://groups.google.com/group/comp.databases.theory/browse_frm/threa...
>
> 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
>(a misleading way if you
> ask me even though I know Date uses them, maybe that's why he concludes
> certain updates are 'unsafe'.
>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:
- One will tell you that lemon is lemon even if its (attribute) color is green.
- 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