Re: Modeling Data for XML instead of SQL-DBMS

"dawn" <dawnwolthuis_at_gmail.com> wrote in message news:1161893884.428842.156110_at_m7g2000cwm.googlegroups.com...
> OK, I'll review all the feedback and come back with a revised question
> (once I have proper definitions for the logical data model and know
> precisely for which model we need to know whether persistence will be
> handled with UniData or DB2, for example).

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

> Only because I need to rephrase the question and am apparently using
> the term Logical Data Model incorrectly, yet I'm not certain whether if
> you and I are both given the same conceptual data model and you are
> implementing it in Oracle and I in UniData, whether we might have the
> same logical data model, although different implementation data models,
> or whether our logical data models would differ. Mine would include
> multi-valued attributes, for example. Thanks for any clarification.
> --dawn
>

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.

    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.

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. Received on Thu Oct 26 2006 - 22:49:17 CEST