Re: How to find Brothers and Sisters?

--CELKO-- wrote:
> >>, I do not recall that Codd's original specification of 1NF allowed NULL. <<
>
> Yep, right from the start in RM1 as rule #3:
>
> 3. Systematic treatment of null values
>
> The DBMS is required to support a representation of "missing
> information and inapplicable information" that is systematic, distinct
> from all regular values (for example, "distinct from zero or any other
> number," in the case of numeric values), and independent of data type.
> It is also implied that such representations must be manipulated by the
> DBMS in a systematic way
I agree CELCO (If I undestood rightly his wrote information). Unknown information almost evry time exists someware. Someone wrote as a sample that NULL is not necessary. UNEMPLOYED & UNKNOWN_JOB.
These Information are clearley different. UNEMPLOYED is one state of a person's current job. His/Her job information is KNOWN as UNEMPLOYED. It is different from UNKNOWN. The person's jon information is UNKNOWN means that he/her has some job or UNEMPLOYED. It is realy UNKNOWN.
Another example is....
Even unpaid SALARY may known the value. For example company is about to fall down and have enough money to pay agreed salary for it's employees.
So, value of SALARY is KNOWN. But, UNPAID. Value of SALARY and it was PAID or UNPAID are information in diffent domain.
More over, thers is a possibility SALARY is UNKNOWN. But it is KNOWN that it is already PAID or not. Received on Wed Jan 10 2007 - 15:59:59 CET