Re: Reminder, blatant ad

dawn wrote:
> Jan Hidders wrote:
>

>>dawn wrote:
>>
>>>OK, then I'm pretty sure there are no such administrative features that
>>>can be performed on most commercial databases today that require a
>>>change to the logical data model.
>>
>>?? Most of them allow me to add indexes w/o changing the logical model,
>>or change clustered indexes to non-clustered ones, for example.

Ah, yes I did. But then, depending on what you define as "the logical model", your observatoin is besides the point. This is not what distinguishes DBMSs that feature physical data independence from those that don't. For example, in the extreme case where there is no physical data independence and the logical and physical model therefore coincide, the only way to change the physical model is by changing the logical model, and so even in that extreme case there are no separate administratieve features that require a change to the logical model.

> Any ideas on a VSAM example of where a physical model change would
> prompt a logical data model change? (that was at the end of this
> message)

Well, if the fact that your data is stored in VSAM files is part of the logical data model, then if you would change that to, say ISAM files, then you would have to change the logical data model.

• Jan Hidders