Re: How to normalize this?

On 2013-05-01 16:08:17 +0000, Erwin said:

> Op woensdag 1 mei 2013 17:38:17 UTC+2 schreef Jan Hidders het volgende:

>>> Op woensdag 1 mei 2013 11:20:47 UTC+2 schreef Jan Hidders het volgende:

>>>> On 2013-04-30 22:17:44 +0000, Erwin said:

>>>> 

>>>> And I would argue that in practice the different>> components usually

>>>> turn out to be independent facts anyway. The fact>> that they have

>>>> different underlying dependencies already sort of hints>> at that. But

>>>> if you have a realistic example that would show otherwise,>> that would

>>>> be interesting.

>>> 

>>> Not sure if I'm thinking of the same kind of thing as you, but I'm

>>> thinking of CUSTOMERs that have an AGE, where AGE determines [some kind

>>> of] COMMERCIAL _CLASS.

>>> 

>>> AGE and COMMERCIAL_CLASS don't become facts that are "independent" from

>>> there being a CUSTOMER to begin with.

> 
> :-)
> 
> You responded only to the piece of which I wrote myself :
> 
> "Bad example.  pls disregard."
> 
> Does the "_there_ we probably differ" imply then that you agree with the rest ?

To some extent. I certainly agree with the observation that when reasoning about update anomalies and redudancy we should take all database constraints into account, not just functional dependencies. But I still don't follow you where you state that in OP's original example this is necessarily an issue. It could be, theoretically, but I doubt it happens often in practice.

• Jan Hidders