Re: Object-relational impedence

On 2008-03-04, Dmitry A. Kazakov <mailbox_at_dmitry-kazakov.de> wrote:
> On Tue, 04 Mar 2008 19:45:30 GMT, David Cressey wrote:
>
 <snip>
>>
>> This is true for an RDBMS. But more to the point, can a relational (or
>> SQL) database be designed in such a way that it has moderately good support
>> for thousands of anticipated queries, of which only a few dozen will
>> actually come to be used ? And will those few dozens of uses provide the
>> appropriate payback on the investment in building the database?
>
>> Based on my experience with databases, I offer the firm opinion that the
>> answer is yes.
>
> That's OK to me.

Good.

> But the question, as I understood it, was about
> qualitative design changes. My point was that there is always a presumption
> of the nature of changes which can and of those that cannot happen. A
> design is good when this presumption matches the reality. From this point
> of view there is no difference between deployment of OO or RDB solutions.
> As engineering both would solve some class of problems and anticipate
> quantitative changes of certain kind, but not qualitative ones.
>
> When I read what Eric wrote, that made me think that he believed that RDB
> would solve all problems and thus anticipate any changes. This would be
> obviously wrong.

I don't believe that merely using an RDBMS will solve all problems. What I meant was that, accepting what David said above, if you keep your data in an RDBMS, it will be easily available for the solution of any possible problem that can be solved using that data.

> I guess that his hidden argument was "because RDB
> apparently solves all problems, then data-centric view is the right one."

No, the argument is that the data-centric view is often (not necessarily always) the right one to take, and that keeping the data in an RDBMS provides a better basis for solving future problems using the data than any other way of keeping it.

> Yet another logical fallacy was a data-centric problem statement: "there
> will never be any other application that will need my data," used in order
> to prove data-centric view itself.

There is no fallacy here. First there is a fact - you have data, however you choose to view it. Do you want to deny this? If you do we may need to sort out the meaning of the word "data". Given this fact, I am saying that you can not guarantee that there will be no other uses for your data, so you must keep open a way for those other uses to see your data.

> In OO problems are not modeled in terms
> of applications using data.

No, but the data is still there.

> This alone does not yet imply anything about
> the problems being solved. Actually we all are solving similar problems,
> otherwise there would be no such quarrel between us.
>
> P.S. OO is especially focused on maintenance. H.S. Lahman already wrote
> about it in another post, so I need not to repeat it here.
>

E Received on Wed Mar 05 2008 - 12:34:05 CET