Re: I have read tons of theory...but still...one question

> I'm sorry to make a simple example complicated. But here goes.
>
> In the case of land lines (Work, Home phones) the "telephone number"
> does
> not identify a telephone. If I unplug the telephone in my house, take it
> over to your house and plug it in, it no longer has any relationship to
> my
> telephone number.
> In other words, a telephone does not "know its own number" to
> anthropomophize a bit.
>
> In the case of cellulars, a phone knows it's "contract number" in
> America.
> In Europe, think there's a card inside to phone that knows its contract
> number. The contract number determines the phone number.
>

Alright, but this goes a little bit too far for my purposes. A phone essentially means a number at which a person can be reached.

> Next,
>
> I take it that PhoneID and ActualNumber are both candidate keys. If
> ActualNumber is NOT a candidate key, then I think you have transitive
> dependencies and therefore the relation is not in 3NF.

Yes that is correct, they both are.

>> numbers. So I create a>>
>> Obviously, however, there is some redundancy in having the three values
>> of
>> the PhoneType attribute repeating for thousands of records containing
> phone
nother table
>> PhoneType (PhoneTypeID, PhoneType).
>
> I'm not sure I really get what you are saying. It sounds like you are
> concerned about physical redunancy
> (too many bytes in the value), rather than logical redundancy (the same
> fact in more than one place.)

Yes, physical redundancy and also the case of mispellings. If I store the phone types once and correctly I dont need to worry whether there will be a mispelling in entry of one fact such as "CelPhone" instead of "CellPhone" or "Cell_Phone".

> If that's what you are thinking, then you are vulnerable to what I'll
> call
> a "Neo Con" (being conned by Neo).

The only Neo I know is the one from Matrix :-)

Thanks

Konstantinos Received on Fri Oct 15 2004 - 20:13:56 CEST