JOG wrote:
> Bob Badour wrote:
>
>>JOG wrote:
>>
>>
>>>topmind wrote:
>>>
>>>
>>>>Nulls are a vendor-specific idea, not inherent to relational.
>>>
>>>While I agree with much of your post, nulls now appear to me to be
>>>essential to the relational model (whatever their rights and wrongs).
>>>If one fully normalizes a database then it is likely a join will
>>>require the use of null to pad the resulting virtual relation. Just
>>>because these relations are not persisted on disk, makes them no less
>>>'relations' in the sense of Codd's algebra. As such i am currently
>>>struggling with how one can be against nulls (as per Date's perfectly
>>>justified view) but pro-RM from a completely theoretical standpoint.
>>
>>With all due respect, is it possible you confound NULL with missing
>>information?
>
> Quite possibly Bob, and if so I stand corrected. I was referring to
> fill values generated via outer joins, which are of course not
> synonomous with the black holes that are SQL NULLS. I presonally avoid
> external joins as much as possible, but they seem prevalent enough that
> (if I recall correctly) they figure in Date and Darwen's D.
I suspect, where people currently use outer joins, they generally would
prefer a relation valued attribute in any case.
Received on Mon Apr 17 2006 - 09:12:09 CDT
