Re: Demo: Modelling Cost of Travel Paths Between Towns
Date: 14 Nov 2004 17:52:39 -0800
Message-ID: <4b45d3ad.0411141752.2459ac4c_at_posting.google.com>
> > Yes, a separate table for states is the correct way to avoid redundant
> > PA's (even if PA doesn't have any properties). Alan didn't provide
> > such a schema thus he has redundant PA's.
>
> States do not need a seperate table because (at this point, anyway)
> they have no properties.
A separate table for states is need to avoid redundant PA's. Your current schema has redundant PAs. The first PA represent PA. The second PA also represents the same PA as the first. According to CJ Date, redundancy leads to update anomalies. Assuming no auto-sychronization, your db can be corrupted by modifying one of the PAs. Please reread chapter 10 and in particular pg 312 of "An Intro to Db Systems" 6th Ed. Received on Mon Nov 15 2004 - 02:52:39 CET