Re: Another view on analysis and ER

From: David Cressey <cressey73_at_verizon.net>
Date: Fri, 07 Dec 2007 20:36:05 GMT
Message-ID: <V8i6j.261$Bg7.223_at_trndny07>


"TroyK" <cs_troyk_at_juno.com> wrote in message news:ac66edf3-bc57-47c4-9327-c41be3911dc0_at_l1g2000hsa.googlegroups.com...
> On Dec 7, 1:42 am, Jon Heggland <jon.heggl..._at_ntnu.no> wrote:
> > Quoth rpost:
> >
> > > David Cressey wrote:
> > >> Bingo! That's the big problem with the literature on ER. Many ER
> > >> proponents use ER as if it were a design artifact. I think that 's a
> > >> misapplication of the artifact, and I'm pretty sure Peter Chen would
agree.
> > >> If one is designing a relational system (including but not limited
to a
> > >> relational database) then using the relational model to capture the
design
> > >> is a much better idea.
> >
> > > Well, that reflects what "we" teach: make a model in ER then convert
it
> > > into a logical relational design. I thought it was how ER is *always*
used.
> >
> > But this conversion is fairly mechanical. Is "design" in this case just
> > the little bit of human input that enters this process?
> > --
> > Jon
>
> For any given conceptual model (assuming in this context
> that we take the ER model mentioned to be a conceptual
> model), there are (usually) more than one valid logical designs
> that will faithfully model it.
>
> The act of choosing among the tradeoffs that those logical
> models imply, to me, is the act we call designing.

Exactly.

> I'm unaware
> of any tools that do this mechanically (at least adequately),
> so I would say that the human input is more than a "little bit",
> which you said.
>

Data Architect from Sybase did this for me very well back in 1999. It did physical design in the same step, but no matter. Received on Fri Dec 07 2007 - 21:36:05 CET

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