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Re: model inherited object

From: <deja_at_2bytes.co.uk>
Date: 24 Jun 2006 01:56:54 -0700
Message-ID: <1151139414.232217.101250@p79g2000cwp.googlegroups.com>


 You seem to take it as axiomatically true that any change recorded for
> year x must necessarily also be recorded for all years x+n. I
> disagree.
>
> If the user wants to change some recorded facts about the past, then it
> is *his* responsibility to specify *precisely* what the period of time
> is for which he wants to change those recorded facts.

well i disagree with this. It's not necessarily the past if x is present and x+n is in the future. But i get the general gist that this is not resolvable, the use of a calendar table as suggested by Celko only works if you've got a history table per attribute I think.

thanks to everyone for the discussion though

Erwin wrote:
> > So I record tuple X as (ID,Sq Ft, Toilets, ValidFrom) as LOC01 - 200 -
> > 2 - 2005.
> > Because of the building work I will record tuple Y as LOC01 - 400 - 2 -
> > 2005 but in fact those 2 toilets are inherited and should be reflected
> > if I ever update the 2005 record. ALSO I want the 2006 database to show
> > me the relevant details (which in this case is 200 sq ft and 2 toilets
> > because it hasn't changed since 2005).
>
> You seem to take it as axiomatically true that any change recorded for
> year x must necessarily also be recorded for all years x+n. I
> disagree.
>
> If the user wants to change some recorded facts about the past, then it
> is *his* responsibility to specify *precisely* what the period of time
> is for which he wants to change those recorded facts. And the system
> must both allow and force the user to do exactly that. It's not the
> system's task to decide on the timespan for which some update is valid.
>
> > Thanks for any advice
>
> I'm afraid there's only one really useful advice to be given here : if
> you're looking at *data*, then put off those damn OO glasses they gave
> you when you were born. It will help you to see clearer. E.g. in a
> database context, there is little true meaning in statements such as
> "toilets are inherited".
>
> And if "putting off those darn OO glasses" implies that you are left
> without a vocabulary to express yourself, well, that's a strong
> indication that you still have a lot of relevant vocabulary to learn.
> Date's "Introduction to ..." is not that bad a place to start and learn
> it.
Received on Sat Jun 24 2006 - 03:56:54 CDT

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