Re: What does this NULL mean?

"David Cressey" <dcressey_at_verizon.net> wrote in message news:K2Qnf.2517$0z.2002_at_trndny02...
>
> "mountain man" <hobbit_at_southern_seaweed.com.op> wrote in message
> news:ttrnf.19034$ea6.17392_at_news-server.bigpond.net.au...
>
>> Dependent upon the measure of complexity of your database
>> it may be argued that the design is never complete because it
>> is under constant evolution.
>
> [snip]
>
> Your post is outstanding, perhaps the best I've read in this thread.
>
> I think "change management in databases" deserves a discussion of its own.

There has been limited discussion here, and there are articles about on this issue under the keyphrase of "schema evolution".

The issue is avoided by Date et al (AFAIK) whereas it is precisely this issue of schema change that should be subject to the principles espoused by the relational model.

The RM guides the design of new databases, and it obviously also must guide the evolution of old databases, but this aspect has not yet been thrashed out in any formalised manner.

-- 
Pete Brown
IT Managers & Engineers
Falls Creek
Australia
www.mountainman.com.au/software