Re: Modeling question...

From: David Cressey <cressey73_at_verizon.net>
Date: Fri, 25 Jul 2008 16:29:25 GMT
Message-ID: <Fbnik.20$rb5.6@trnddc04>

"Volker Hetzer" <firstname.lastname_at_ieee.org> wrote in message news:g6cmjq$9s9$1_at_nntp.fujitsu-siemens.com...
> Bob Badour schrieb:
> >>> Ooooh! Reinventing EAV with levels...
> >>
> >> Possibly. I had a look at
> >> http://ycmi.med.yale.edu/nadkarni/eav_CR_contents.htm and didn't find
> >> anything exciting.
> >> All my attributes (key value pairs) are (for the purpose of this
> >> discussion) strings, so the Data tables hierarchy ends with
> >> EAV_Objects in the first image of that link.
> >> My problem is that, that I haveTest three different "Objects_1"
> >> tables and I'd like to avoid having to replicate the EAV_Objects-Table
> >> for each "Objects_1"-Table.
> >> OTOH, I could have the "level" entities all be children of an id table
> >> and
> >> put the key value pairs into a child of that table. I need to try this
> >> out.
> >>
> >> Thanks for providing the pointer!
> >> Volker
> >
> > Just to be clear, I was more than offering a pointer. I was also
> > ridiculing the idea of EAV.
> I got that. :-)
> But "we want to be able to create and delete attributes" is a customer
> requirement. I think it's different from "I am too lazy to do a proper
data
> model". There are plenty of "normal" attributes left to model ERD like.
>

Here's the problem with the customer requirement that "we want to be able to create and delete attributes": the same customers nearly always want to be able to derive value from the data in the database by using it with standard queries to drive standard reports, charts, or extracts that can be fed to another process. After all, that's inherent in database data, isn't it? Well, not if the customers can each invent their own attributes, it isn't!

If you've never been down this road before I suggest you stay in the same job long enough to see what happens when you tell the customers that each of them has to design their own queries, because each of them defined their own attributes. What happens isn't pretty!

> Lots of Greetings!
> Volker
> --
> For email replies, please substitute the obvious.
Received on Fri Jul 25 2008 - 11:29:25 CDT

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