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Re: The wisdom of the object mentors (Was: Searching OO Associations with RDBMS Persistence Models)

From: David Cressey <dcressey_at_verizon.net>
Date: Fri, 02 Jun 2006 12:43:57 GMT
Message-ID: <hoWfg.1250$DO5.793@trndny06>

"phlip" <phlip2005_at_gEEEmail.com> wrote in message news:pan.2006.06.01.21.15.18.59187_at_gEEEmail.com...
> Bob Badour wrote:
>
> >> An application should have its SQL statements in only a few modules,
and
> >> all others should be SQL-free.
> >>
> >> Note in my statement, you can replace SQL with GUI, XML, ORB, etc, to
> >> generally the same effect. The point of modules is to isolate and
> >> encapsulate.
> >>
> >> Is that so hard?
> >
> > Define: few
>
> Encapsulation is hierarchical. The longer the conceptual distance between
> any two points in a program, the narrower their communication should be,
> if any.
>

I'm lost with "conceptual distance".

Here's a scenario. We look at four modules (out of hundreds) in a large hospital data magement system.

One module massages data about health insurance, credit cards, and reimbursement. It is written in Java.
A second module exchanges data with the DBMS about health insurance, credit cards, and reimbusement from the . It is written in SQL, with a thin wrapper of Java.
A third module exchanges data with the DBMS about clinical histories, patient privacy, and compliance with privacy law. It is written in SQL, with a thin wrapper of Java.
A fourth module massages data about clinical histories, patient privacy, and compliance with privacy law. It is written in Java.

It sounds from what you've said above as though the "conceptual distance" between modules 2 and 3, and between 1 and 4 is short, while the "conceptual distance" between modules 1 and 2, and between 3 and 4, is long.

This makes no sense to me.

> So the few modules that have SQL in them should have wider communication
> with each other than with others. Sometimes we call that a "Layer".
>
> Define: wider, longer, narrower, sometimes, etc. Answer: When you don't
> mix SQL in with your GUI, XML, ORB, and other what-not modules.
>
> The alternative is like Visual Basic kiddie-kode, with multiple rampant
> SQL statements inside every button event handler. That's bad, so don't do
> that!
>
> Define: bad
>
> :-(
>
> --
> Phlip
Received on Fri Jun 02 2006 - 07:43:57 CDT

Original text of this message

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