Re: We claim that delete anomality is due to table not being in 3NF, but...
Date: Fri, 31 Oct 2008 06:46:53 -0700 (PDT)
On Oct 30, 11:23 pm, Hugo Kornelis
> On Wed, 29 Oct 2008 22:59:25 GMT, paul c wrote:
> >Hugo Kornelis wrote:
> >> Functional dependencies stem from reality. Whether or not you choose to
> >> include B in your model does not change the situation where, apparently,
> >> C depends on A through some intermediary B (that is not in the DB).
> >> In a DB that stores PersonID and EyeColour, one might argue that the
> >> actual dependency goes back to the parents of the person and their
> >> genetic patterns - but those will typically not be stored, and yet the
> >> EyeColour still depends on PersonID.
> >> ...
> >Assuming you're saying it's improper to depend on any notion of absolute
> >reality, I think I'd agree. Doesn't a db aimed toward aiding some
> >present function necessarily stand for a very fractional/partial (or
> >even distorted) reality? Eg., if it's not fractional it's probably
> >unwieldy and untoward. Seems to me that the EyeColour dependency hints
> >at this - when the purpose of a particular set of tables isn't concerned
> >with dna, one likely ignores blood lines. Further, I suspect that no db
> >ought to introduce fd's that aren't patently implicit in the user's
> >requirements/biz rules/application intent. In the USA, I gather that an
> >address that is complete enough for a mailman to deliver to, along with
> >a city and a state will determine zipcode, yet I suspect there are many
> >tables in non-postal db's that have a column set such as (Customer,
> >unit, streetaddress, city, state, zip).
> Hi Paul,
> This is cdt, not alt.philosophy. I was not after an existential
> discussion on absolute reality. :)
> You're reading way more into my example than I intended. The point I
> tried to make is that functional dependencies are not determined by what
> is or is not stored in the database, but by how entities and their
> interactions in reality. The DB is a model of reality and changing the
> model won't change reality.
I too would disagree that a DB is a model of reality - it is a model of data (i.e. comments about the world from some individual standpoint). That data /already existed/ in the wild, and the DB simply models it in a form amenable to querying and manipulation. Its algebra hence deals with statements and not the items they discuss.
> I already considered the example pretty bad when I wrote it, and now
> that I see what you read into it, I'm really embarassed...
> Best, Hugo
Received on Fri Oct 31 2008 - 14:46:53 CET