Re: Object-relational impedence

From: topmind <>
Date: Mon, 3 Mar 2008 13:57:42 -0800 (PST)
Message-ID: <>

On Mar 3, 10:54 am, Bob Badour <> wrote:
> topmind wrote:
> > JOG wrote:
> >>On Mar 3, 2:07 pm, Thomas Gagne <> wrote:
> >>>All attempts by applications to access a DB's tables and columns
> >>>directly violates design principles that guard against close-coupling.
> >>>This is a basic design tenet for OO. Violating it when jumping from OO
> >>>to RDB is, I think, the source of problem that are collectively and
> >>>popularly referred to as the object-relational impedance mismatch.
> >>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.
> >>I was hoping perhaps people might be able to offer perspectives on the
> >>issues that they have encountered. One thing I would like to avoid
> >>(outside of almost flames of course), is the notion that database
> >>technology is merely a persistence layer (do people still actually
> >>think that?) - I wonder if the 'mismatch' stems from such a
> >>perspective.
> > This came up in a nearby message. I borrowed the following text from
> > wikipedia:
> The text had too many blatant errors to start enumerating them all.

Most of them are statements about philosophy or practice rather than absolutes; thus its hard for them to be objectively or "blatantly" wrong. Whether that's a good thing or not is another issue. I see the list as a starting point for discussion even if it does not settle everything.

It brings up interesting questions, such as why not have schema inheritance? If inheritance is good or OO, why is it not good for relational schema's? The answer is that OO and relational approach things differently.

> The
> problem with wikipedia is any ignorant fool can just start typing
> nonsense. Even when one follows the requirements for references to
> primary sources, the quality of the end product can vary over many
> orders of magnitude.

-T- Received on Mon Mar 03 2008 - 22:57:42 CET

Original text of this message