Re: Modeling Data for XML instead of SQL-DBMS

David Cressey wrote:

> I'm going to suggest that there are at least two conflicting definitions of
> "logical data model" in use in the newsgroup, regardless of what the
> glossary says. One of the definitions might be called "preliminary design".
> The other might be called "programmer visible implementation."

To me, to 'preliminary design' is sketchy, while 'logical data model' carries a connotation of completeness and detail. But I'm sure you are aware that if you provide helpful copy & pastable definitions I'd be happy to include them in the glossary, even if I do not completely agree.

> Note that,
> in the case of design choices that are invisible to the programmer, it
> doesn't matter why they are invisible.

Yes. You mean things like indexes, partitions, pinning, right?

...
> Here's the way I learned the terms, back in 1984 (no pun intended).
>
> conceptual data model (CDM): Driven by requirements. results from data
> anlysis. |data model independent. Example: er modeling.
>
> logical data model (LDM): design model, cannot be changed without (in some
> situations) requiring (some) application code rewrite.

I have never seen (or don't remember) this criterion, but it sounds healthy.

> result of preliminary design, driven by conceptual model, plus some
> indication of how the data is to be used. Data model dependent, DBMS
> independent, with a class of DBMSes that are all based on the same data
> model. Exapmple: relational data model.

The use of 'data model' in this sense may be confusing (when not explicitly stated).

> physical data model (PDM): late design model, driven by logical data
> model, but also by data volume, resources, load, and speed priorities.
> DBMS product (and perhaps version) dependent. Example: p.d.m. for
> implementation on Oracle.
>
> create script: this term makes sense only in the context of SQL DDL, but
> the same idea could be applied to other environments. DDL ready to be run
> by a DBMS to create an empty database.
>
> Note that this terminology survives just about intact, when used with Data
> Architect, pert of Power Designer in 1999. Except that DA doesn't discuss
> an LDM separately. You can think of the table desing in the PDM as being
> the LDM.
>
> I'm NOtT claiming that this terminology is standard, or even the best. I am
> saying that I've been using is to communicate with others for over 20 years.
> And I recommend it for that reason.

-- 
"The person who says it cannot be done
should not interrupt the person doing it."
Chinese Proverb.