Re: Object-relational impedence

From: Roy Hann <specially_at_processed.almost.meat>
Date: Mon, 3 Mar 2008 17:24:20 -0000
Message-ID: <>

"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 the 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.

> What defines an account in an RDB may be composed of multiple tables.
> An RDB might express multiple account types through multiple tables
> where OO may reflect it as multiple classes. Attempts to make RDBs
> function as graphs through mapping tools results in disappointing
> performance and, in my experience, too much mapping, too much
> infrastructure, and too much language/paradigm-specific layers. In
> short, way more code, way more maintenance, and way more job-security
> for consultants, pundits, and tool providers.

I completely, 100% agree with that. Code is evil.

Roy Received on Mon Mar 03 2008 - 18:24:20 CET

Original text of this message