Re: We claim that delete anomality is due to table not being in 3NF, but...
Date: Fri, 31 Oct 2008 00:23:53 +0100
Message-ID: <i7gkg4tfcp09te5vir9ilrgh2ugm106mur_at_4ax.com>
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
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