Re: Critique of Robert C. Martin's "Agile Principles, Patterns, and Practices"

On 26 Jan 2007 17:01:55 -0800, Daniel Parker wrote:

On Jan 26, 4:37 pm, Robert Martin <uncle...@xxxxxxxxxxxxxxxx> wrote:
On 2007-01-26 11:42:52 -0600, freb...@xxxxxxxxx said:

There is no need for passing data structures around the application.
Relations are the only needed data structures. (Sometings performance
issues might force you to use low-level collection classes likes arrays
and hastables, but this is normally not the fact for business
applications.) The application should ask the database for the needed
data, using set theory and predicates, when the data is needed, not
before.

I agree with everything you say there. An object is a relation, and it
is very convenient to use.

"an object is a relation" ??? A relation in relational theory,
consisting of a set of tuples, is roughly analogous to the idea of a
table, consisting of a list of rows.

Relation is an operation over objects in a model which would implement RA.
But also a relation can be an object in some higher-level model. Even SQL
has that level, consider CREATE TABLE as an operation over relations as
object. The advantage of OO is that you can mix models more freely. For
that matter RA is much more limiting framework. Just consider expressing
arithmetic, image processing, or for that matter CREATE TABLE in terms of
RA!

I cannot tell if OO [~ subtyping relation and dispatch] could be
represented in RA. (The reverse is clearly possible) Which would make
Robert's argument *formally* correct. But in spirit it is, being old known:
"we all are Turing-complete, guys."

--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
.

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