Re: Lucid statement of the MV vs RM position?
Date: Thu, 27 Apr 2006 19:19:56 GMT
David Cressey wrote:
> "Pickie" <keith.johnson_at_datacom.co.nz> wrote in message
>>People can collaborate (and exchange data in a meaningful, formal >>fashion) without a DBMS. In practice, using a DBMS involves much more >>than just providing the database(s). You have to be able to evolve the >>database structure for new circumstances, which means you run into a >>different set of problems. But I understand where you are coming from.
> The above is a high cost wish list. I grant that. In order to get
> sufficient bang for the buck, you are going to have to get a lot of utility
> out of the data that you've made this investment in. That's what I think
> the practice of database development is all about.
A good formalism reduces the cost of the wish list. This is as true for data models as it is for discrete signal analysis, vector calculus, grammar specification etc.
> When I'm being careful (wich is not always), I try to use the initials,
> RDM, rather than RM. It's important to remember that the RDM is a data
> model, not just a model. Some people in this forum argue that "NULL" has
> no counterpart in mathematics, so it shouldn't be part of the model. That
> misses the point. If you are building a DATA model, you have to address
> the question: what are you going to do when the data isn't there? as well
> as the question, how do you prevent missing data? That is why Codd
> addresses the issue of missing data, rather than evading the issue.
Actually, I believe Codd tried to instill some formalism to an ad hoc feature thrown in by others. All one has to do to allow for some information to be missing is to structure one's predicates to allow for it.
Null is a toxic elixir. It gives one the illusion of power, and it restrains the minds of those who use it. Received on Thu Apr 27 2006 - 21:19:56 CEST