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

From: Christopher Browne <cbbrowne_at_acm.org>
Date: 17 Oct 2004 05:00:48 GMT
Message-ID: <2tecjvF1vaedaU1_at_uni-berlin.de>


In the last exciting episode, "Kostas" <noemail_at_noemail.net> wrote:
> "Lemming" <thiswillbounce_at_bumblbee.demon.co.uk> wrote in message
> news:8ft0n0p93s2q4o6vu05l19thp2qve9pcnm_at_4ax.com...
>> On Fri, 15 Oct 2004 00:52:18 -0400, "Kostas" <noemail_at_noemail.net>
>> wrote:
>>
>>>Many thanks to anyone who can clue me in,
>>
>> This is not an answer, but a question.
>>
>> Somewhere in this thread someone said to use the phone number as the
>> primary key. Or maybe it was a differnet thread, and that's why I
>> can't find it :) Anyway ...
>>
>> What happens in such a scheme if two people have the same phone
>> number?
>
> Here is the answer (please note I am a novice only compared to the folks
> that frequent this group so it would be better if someone else validated my
> answer).

> The phone number is unique. If our database had only phones we are
> fine as we are. If, on the other hand (and most expected case), we
> also hold information about people that have phone numbers then we
> will also have a second entity PERSON. As such, PHONE becomes a
> weak entity because the existence of a particular phone implies the
> existence of a particular person that owns it.

The phone number is neither unique, nor does it imply the existence of a person that owns it, because:

  1. Multiple people are permitted to use a phone, and
  2. Phone numbers may be tied to companies, or may be reserved for some non-personal purpose. For instance, we have a fax number at the office that has never been associated with a 'person.'

Not very helpful...

-- 
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Received on Sun Oct 17 2004 - 07:00:48 CEST

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