Re: Object-relational impedence
Date: Tue, 4 Mar 2008 03:04:04 -0800 (PST)
On 4 mrt, 00:02, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Roy Hann wrote:
> > "Thomas Gagne" <tga..._at_wide-open-west.com> 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.
> That is a remarkably uninformed and ill-conceived sentence. It's rather
> like comparing boats and cars saying boats have hulls and cars are
> pretty. Regardless of truth, the comparison is pointless on its face.
> One can represent any graph on two-dimensional media just as one can
> represent any relation on two-dimensional media. In fact, since a graph
> is merely a set of vertices and a set of directed edges and since one
> can easily represent vertices and directed edges as tuples, one can
> easily represent any graph using relations.
> The Great Debate was had about 3 decades ago and graphs lost.
I beg to differ. What lost was the idea that a close coupling is required between how the data is stored and how it is accessed / queried, i.e., that in that sense you cannot have data independence. But such data independence can be just as well achieved with graphbased data models.
- Jan Hidders