Re: All hail Neo!
Date: Tue, 25 Apr 2006 12:05:24 GMT
Message-ID: <8go3g.15459$vy1.1811_at_news-server.bigpond.net.au>
Bob Badour wrote:
> Frank Hamersley wrote:
>> 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? >>> >>> No, it is quite explicit. >> >> 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?
>
> Yes, ALL relations are sets of tuples. SQL tables are not relation
> variables and do not contain relations.
>> 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.
>
> RM/V2 seems flawed to me. I am not sure whether I have ever found a
> complete copy of RM/T. Did Codd ever advocate null prior to RM/T? Did he
> ever drop the requirement for logical identity?
I'm not well read enough to be able to hazard answers to these questions. I will does some more reading on these topics after I get off Highway #1.
>> 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.
>
> Relations are elegant, symmetrical and compelling. Bags and null are
> none of those.
>> [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?
>
> Whether nulls exist in the RM today is a topic of some controversy.
>>> Relational algebra is the equivalent of set theory, and relational >>> calculus is the equivalent of predicate calculus. >> >> I have no beef here.
>
> With null or without logical identity, they lack the equivalences
> mentioned.
By logical identity I take it you mean the distinctness of each tuple?
>>> 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.
>
> Shall we get back to this now?
>>>>> 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. >>> >>> Are you suggesting that query transformations lack practical benefits? >> >> No sure where you are going here, can you be specific or illustrate?
>
> The equivalence between relation values and boolean values facilitates
> certain query transformations such as between a union and an 'or'
> predicate and vice versa.
OK. Obviously useful for the theorist to explore stuff (apols to Alexi).
>>>>> 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 >>> >>> {} is the empty set and is the set with cardinality 0. >>> {{}} is the set containing an empty set and is the canonical form of >>> all sets with cardinality 1. >>> {{},{{}}} is the canonical set with cardinality 2. >>> http://www.math.psu.edu/simpson/papers/philmath/node17.html >> >> 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 ;-)
>
> Goedel established limitations to formalism as the foundation of
> mathematics, and I am not sure that philosophy is meant to have an
> endpoint.
Which I find (philosophy) much more interesting these days, although much of it beyond me as a casual investigator.
>>> 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.
>
> LOL
One the few occasions I can say I wish I had said that - and did!
>>> 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.
>
> One wonders in what way they are distinct. Is 1 distinct from 1? Is 0
> distinct from 0? Obviously, as values, they are indistinct. One must
> then posit that they differ in location.
So {1} and {1} are not distinct when conceptually imagined in an OO instance frame of mind? Thus it would take something like {1,2} and {1,3} at which point the sets are distinct? In this case are the 1's distinct?
> However, a single attribute
> within a single tuple within a single relation variable has a unique
> logical location.
True.
> How then can null equate to two locations?
> What then
> does it mean when the null appears in a derived value which has no
> location at all?
>>> 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.
>
> If null is not the same as false, then it is not the same as {}. Does it
> then have an equivalent set representation?
[..]
>> 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).
>
> I suspect your statement is true of all of mathematics and in fact of
> all fields of study.
Which is why we two are assembled here today - not enough of us for a riot however!
>>>> * (for another post perhaps) I don't see any great leap forward in >>>> the aspects of TTM that address the extinction of nulls. >>> >>> If nulls cause great damange without serving any particularly useful >>> purpose, why should one address their extinction? >> >> 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.
>
> Are you familiar with Date's various _Writings..._ books? He and Darwen
> and others have demonstrated that null causes great damage.
I don't need them to postulate it as I've seen it first hand. My opinion of Date mainly and Darwen to a much lesser extent (more by association than real research) is that whilst they have taken a pot shot at a low flying albatross, they haven't come up with anything even close to better. Being too tight to pay them for their various treatises means that I prolly have limited information to base that view upon but what I have seen doesn't thrill me one bit. Hence my 155 mm post on the BM thread.
> Nulls attempt to address missing information but do so with no basis in
> theory. I suggest that the null elixir only offers the illusion of power:
> http://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD898.html
>> 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.
>
> Missing information is messy, and we lack any theory to address it.
> Pretending otherwise may put the mess out of sight and out of mind, but
> that just makes the mess worse and the problems more surprising when
> re-discovered.
Cheers, Frank. Received on Tue Apr 25 2006 - 14:05:24 CEST