Re: Date, Darwen, Pascal and the alternative to Nulls in the RM

I have also been making my way through Date's books. I'm afraid some basic concepts still elude me. Any way, I have been also trying to read some logic books to get a deeper feel for RM. Isn't following a solution to the null problem:

Consider a relation (relvar?):
[social security number, name, age, grade]
(where soc number is the primary key).
Isn't this exactly the same (in logical terms) as:
[soc number, name]
[soc number, age]
[soc number, grade]

The primary key can't be a null. name, age and grade may be safely 'null' (they simply don't exist) in the second representation. The user may still see the first representation (perhaps views?), and if he/she enters a null for one of the non-primary-key fields, the actual logical model simply doesn't 'insert' the null value into its relevant table (eh...relvar).

I've avoided using the term normalization because I'm even less sure of its meaning then other stuff I've written.

Does this make any sense? Received on Wed Mar 22 2006 - 16:49:44 CST