Re: All hail Neo!

Bob Badour wrote:
> Frank Hamersley wrote:

>> Bob Badour wrote:
>>> Frank Hamersley wrote:
>>>> Bob Badour wrote:
>>
>> [..]
>>
>>>>> In that line of thought, here's an interesting question that Date 
>>>>> et al have posed before to the n-VL folks:
>>>>>
>>>>> If "exists but empty" is true and "doesn't exist" is false, what is 
>>>>> null?
>>>>
>>>> Neither and both!
>>>
>>> I find that sort of handwaving to be a complete non-answer.
>>
>> I suspect you are wearing the darkly tinted glasses of preconception. 
>> Whilst I was trying to show a little wit, the current 3VL state of 
>> affairs still seems to me to fit that description.
>>
>>> A much more intellectually honest reply would be: "I don't know."
>>
>> Not from this black duck (on this occasion)!
>>
>>> or "Null has no similar analog in set theory."
>>
>> I wasn't comparing/contrasting the RM with set theory.  Perhaps for 
>> you it is implicit?

I am quite interested in exploring this area so please bear with me as my analysis is heavily tainted with practical experience and less (recently) so with formal theoretical studies. My response may be somewhat affected by the serial reading and responding to your post and I never feel comfortable with long posts when it finally is time to click send!

> Relations are sets.

ALL relations are sets? My gut feeling is that this is not true. I recognise that I hold to this because I view it from the damaged goods position (aka SQL) or the RM as propounded by Codd, rather than from a sounder theoretical starting point. I understand this puts us at odds from inception. From there I expect anything brought to this issue by theory will be elegant, symmetrical _and_ compelling.

[2nd editing]
Having read the texts, below I felt inclined to retract the above para, but then decided to leave it so you could form your own view on how wacky my thinking might be. That said perhaps the fact that nulls do exist in the RM today taken with your confirmed view that they shouldn't (from a theoretical basis) is implied confirmation of my rather unlikely original thought...he says stepping back two full paces - did I write that?

> Relational algebra is the
> equivalent of set theory, and relational calculus is the equivalent of
> predicate calculus.

I have no beef here.

> Thus, the equivalence of dee and true and of dum and false are very
> important. And the question of what relation value equates to null is a
> very good question.

Lets put that aside until the first question has been addressed.

>>> True and 1 both have the exact same analog in set theory. False and 0 
>>> both have the exact same analog in set theory.
>>
>> Perhaps but insistence on a parallel form for the RM does not seem to 
>> lead anywhere practical*...FWICT.

No sure where you are going here, can you be specific or illustrate?

>>> This has a certain elegance and symmetry.
>>
>> I agree that and readily subscribe to that in my own endeavours.
>>
>>> In canonical form:
>>>
>>> {} = 0 = false
>>> {{}} = 1 = true
>>>
>>> What is the similar analog for null?
>>
>> My prior knowledge of your/the notation is non existent but I can 
>> prolly deduce its intent.  So having a stab at it how about ...
>>
>> {}{} = null

Interesting read. However it seems the jury is not even cloistered yet! I quote "The implications of this idea are not yet fully understood and are a topic of current research". Of course, this is from a web page ;-)

> One can continue in this vein until Goedel stomps on one.
> http://en.wikipedia.org/wiki/G%C3%B6del%27s_incompleteness_theorems

OK - it reminds me of a statement made in undergrad science that "you don't prove a hypothesis, you can only disprove it". Of course Godel is more complete than that.

> With respect to {}{} either it is completely meaningless, or perhaps you
> intend the juxtaposition of two sets to mean conjunction or disjunction,
> in which case:
> {}{} = {} = false

It was just a wild punt - the intent was to suggest that two empty sets were distinct and that their intersection was indefinable.

> If null and false are the same, we can do away with null.

They aren't but I guess it may be feasible to do away with null in the truth table ie. null implies false. I expect you would still need its physical presence in the manifestation of tables/relations.

>> As an aside (and with no malice aforethought) I am curious why the 0 
>> and 1 figure at all?  Forced to conform I would probably go with ...
>>
>> {}{} = -1 = null

Thanks for the pointers - admittedly I have only limited time and have had to skim through the material, however it was apparent that there remains substantial areas where consensus has not been achieved (yet).

>> * (for another post perhaps) I don't see any great leap forward in the 
>> aspects of TTM that address the extinction of nulls.

No quite sure what your thrust is here, perhaps you would like to edit it given the damage (sic) it has suffered? In advance of that, I can state that I don't hold that nulls cause _great_ damage (although neither does Semtex in capable hands for a proper purpose) and I certainly believe (at this point) that they do serve a purpose. As to Date and Darwens attempt to remove nulls as shown in the Tutorial-D slides it didn't seem to meet the elegance or compelling stature I mentioned before.

Cheers, Frank. Received on Mon Apr 24 2006 - 06:43:36 CEST