Re: candidate keys in abstract parent relations
Date: Thu, 19 Jan 2006 17:14:55 GMT
Message-ID: <jOPzf.284260$2k.234827_at_pd7tw1no>
Forrest L Norvell wrote:
Right, I think. Very common for "keys" to be re-used. That's why the
biggest Canuck 'phone company used to send two bills if a customer had
two phones and airline systems are complicated because IATA allows a
flight number to be re-used the next day and cash registers re-use
transaction numbers if the power cord is pulled.
The original post mentioned candidate keys which seems to me to be the
important ingredient. I can't see anything wrong with having two of
them in the same relation, eg., {Number} and {Title, Label,
ReleaseDate}, ie., they are 'one-to-one'. Use {Number} in the other
tables. If you ever discover that the other candidate key is
insufficient, you can 'extend' it with a single table change. Depending
on what users want to know, you might not even have to change any queries.
> ...
> Also, on a more abstract level, I'm trying to derive a method for
> dealing with similar problems in the future. It seems to me like this
> is a common problem when trying to model real-world domains,...
(I forget who said you can solve any problem with enough indirection but it seems to apply here).
p Received on Thu Jan 19 2006 - 18:14:55 CET