Re: Object-relational impedence

From: David Cressey <>
Date: Mon, 03 Mar 2008 17:36:50 GMT
Message-ID: <SGWyj.2671$4D2.1906_at_trndny06>

"Roy Hann" <specially_at_processed.almost.meat> wrote in message
> "Thomas Gagne" <> wrote in message
> > JOG wrote:
> >> I wondered if we might be able to come up with some agreement on what
> >> object-relational impedence mismatch actually means. I always thought
> >> the mismatch was centred on the issue that a single object != single
> >> tuple, but it appears there may be more to it than that.
> >>
> > The issue as I've discovered it has to do with the fact OO systems are
> > composed of graphs of data and RDBs are two-dimensional.
> RDBs are not two-dimensional, they are n-dimensional. You are confusing
> picture of the thing with the thing. I have a three dimensional kitchen
> table. I have an RDB table with three columns (dimensions) called length,
> width and height that describes it.

Stop! You're both right!

There is a certain level of abstraction where and RDB is definitely n-dimensional. This is the level of abstraction where I spend most of my time thinking. So I tend to agree with you, Roy.

There is, however, a different level of abstraction where an RDB is two-dimensional. So Tom is not "wrong" all the way. And it may be at that level of abstraction where the OO RM impedance match comes about.

> I completely, 100% agree with that. Code is evil.
It appears, from reading c.o., that OO people regard data structures as evil.

It sounds like Stalinists versus Trotskyites to me! Received on Mon Mar 03 2008 - 18:36:50 CET

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