Re: Lucid statement of the MV vs RM position?

dawn wrote:
>
> OK, so you told me the jury was out regarding modeling and implementing
> with non-1NF data (or something like that);

Not exactly. What the jury is out on is whether you can still have both efficiency and data-independence at the same time, which requires powerful query optimization.

> then I told you that there
> are production systems out there, if the jury really wanted to know;

The jury knows. :-)

> then you said they have already gathered data; then I tried to ask
> "where is it?"; and you said "I don't know any, nor do I expect
> something like that to exist."

... in a published form that you can Google for. But that data is there in the sense that you can talk to experienced developers and DBMS implementors.

> So, I think we talked past each other on that one. If RVAs and other
> non-1NF structures are now accepted in theory and implemented in
> practice, then when should they be used?

When they bring you closer to your goals, such as for example flexibility and efficiency. Whether that is the case or not may depend upon the DBMS you are using.

> If we are going to (re-!)introduce nested structures, we should have a
> good idea when a logical data model should include them, or at least
> know some best practices. If a particular DBMS is not up to the task
> of working well with performance or ease of queries with the nested
> structures, then perhaps the actual implementation needs to normalize
> (1NF). But I'm not seeing nested structures yet in logical data models
> (not that I'm seeing all LDMs).

To add some confusion; there actually is such a thing as *the* logical data model, called LDM. Google for "logical data model kuper vardi". But I digress.

But what do you mean with "I'm not seeing nested structures". Are we talking about conceptual data models? About database schema designs in practice? Proposed data modelling notations? Or what?

• Jan Hidders