Re: Multiplicity, Change and MV

x wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:p461g.61678$VV4.1151995_at_ursa-nb00s0.nbnet.nb.ca...
>

>>x wrote:
>>
>>
>>>"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
>>>news:tx51g.61657$VV4.1151645_at_ursa-nb00s0.nbnet.nb.ca...
>>>
>>>
>>>>x wrote:
>>>
>>>>>There is nothing bad about nulls.
>>>
>>>>I suggest you check out the various _Writings..._ books by Chris Date.
>>>>The flaws in NULL and NVL for N > 2 have been well-argued.
>>>
>>>They have been argued in prose. I prefer mathematics.
>>
>>SUM(A) + SUM(B) = SUM(A+B)
>>
>>unless either A or B can contain NULL. If you think none of the
>>arguments are mathematical, I suggest you re-read them.

No thank you. I have already explained this one multiple times online. Perhaps you can find my prior explanations using Google Groups.

Otherwise, I will leave it as an exercise for the reader. If you want a starting place for the definition, I suggest Codd's RM/V2 as a better starting point than the definition of SQL.

However, if you want to propose and advocate an alternative to the relational model based upon some different logic, by all means do.

> I have not thought hard enough about it, but I suspect Codd had.

However hard Codd thought about it, I suggest he did not think hard enough. Then again, perhaps he did and published his suggestions so someone else could overcome the difficulties he encountered.

>>>Actually using only 2 values feels like using machine code. :-)
>>>I see nothing wrong using a boolean algebra with uncountable many

>>>This in theory. I practice things may differ.
>>
>>Again, the purpose determines the utility. I recall examples by Codd
>>that make heavy use of graph theory; although, the RM does not.

>>If you think relational proponents reject mathematics, you are a fool.

Enough for what? I do not know enough mathematics to prove Fermat's Last Theorem. I do know enough to compare proposed logical data models, to understand the predicate calculus and set theory upon which the RM is based, to effectively use Maxwell's and Shroedinger's equations etc.

Although, I am sure if you search hard enough, you will find advocates of just about anything who do not understand what they advocate. In fact, I doubt one will have to search all that hard.

>>>>>Only the SQL style null is bad.
>>>>>You can choose if you prefer to use relations with nulls or sets of
>>>>>relations.
>>>
>>>
>>>>Unfortunately, if your DMBS has to allow for NULL, it will generally not
>>>>function as well as one that does not. Even if the DBMS implementation
>>>>detects all cases without NULL for optimization purposes, the DBMS will
>>>>require more executable code and have more branches of execution. As a
>>>>general rule, these properties will translate into slower code (ie. more
>>>>page faults) and buggier code (ie. less complete coverage during

>>>Write once, debug a lifetime, die. :-)
>>>In theory a DBMS will not have bugs. :-)
>>
>>Actually, in theory a DBMS will have bugs. Every human artifact has
>>flaws. The important things to consider are failure modes, ease of
>>detection, and chance of recovery.

>>Even if one uses correctness proofs for every piece of code, humans have
>>been known to create flawed proofs.

>>Human failure drives many data management principles like the relational
>>prohibition against subversion.

Pure mathematics is entirely experimental. I am less sure about applied mathematics. Received on Tue Apr 18 2006 - 17:45:16 CEST