Re: Does Codd's view of a relational database differ from that of Date & Darwin? [M.Gittens]

"Eric Junkermann" <eric_at_deptj.demon.co.uk> wrote in message news:u$GfI$CFpYoCFwUa_at_deptj.demon.co.uk...
> In message <3R6oe.1962$F7.1337_at_news-server.bigpond.net.au>, mountain man
> <hobbit_at_southern_seaweed.com.op> writes
>>
>>There have been, there are,
>>and there always will be
>>NULLS in the real world.
>>
>
> Definition and examples, please.

IMO I view nulls as a void representing incomplete information that arises because that information is not (yet) available to the DBMS, for various reasons.

It could be that the data has been deleted. It could be that it has not yet been entered. It could be that it was missed by data entry.

It could be that a power outage caused an incomplete transaction in a DBMS that does not have transaction audit capabilities, such as Access, or a number of larger systems.

In the real world various things prevent the total gathering of information and the process whereby that information is entered and then maintained in the database.

Thus I view nulls as a void representing the fact that there exists incomplete or missing information.

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