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

From: Kostas <noemail_at_noemail.net>
Date: Sun, 17 Oct 2004 02:44:15 -0400
Message-ID: <10n47jo7k4inadc@corp.supernews.com>

I guess we are talking from a slightly different perspective then. In my database I have people and phones. A phone may belong to a person, two or three. As long as the phone is a weak entity I dont see what the problem is when a phone number is associate with one or multiple people, since the PK will always be Person and Phone.
Am I wrong?

Konstantinos

"Christopher Browne" <cbbrowne_at_acm.org> wrote in message news: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:
>
> a) Multiple people are permitted to use a phone, and
>
> b) 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...
> -- 
> (reverse (concatenate 'string "ofni.secnanifxunil" "@" "enworbbc"))
> http://www.ntlug.org/~cbbrowne/linuxdistributions.html
> "The American Republic will endure until the day Congress discovers
> that it can bribe the public with the public's money"
> -- Alexis de Toucqueville 

Received on Sun Oct 17 2004 - 01:44:15 CDT