Sunday, August 11, 2013

Site Update

A while ago my friend Stephen Henley published his opinion on Missing Data, which questioned the thoughts--not well formed and definitive at the time--of C. J. Date, Hugh Darwen and myself on the subject. Since then Date has proposed a default values scheme which he has subsequently renounced; Darwen has published How To Handle Missing Information Without Using NULL and I proposed a relational solution in the recently revised paper #3, The Last NULL in the Coffin.

In this context, I dedicate this update (except the last item) to NULL. Whatever difference may exist among the above mentioned relational proponents, we do agree that it is certainly not a solution to the problems of missing data.

Time permitting, I may post some belated comments on Henley's piece.

If SQL is based on relational algebra which is based on set theory where the concept of null set (empty set) is an axiom of the theory. In this theory empty set is not the same thing as nothing. A point that confuses many people.

Relational algebra is based on 3VL predicates, that is, the answer to any predicate can have three states true, false or unknown. Unknown is caused by the use of a operator on an the absence of a value (null). Within relational algebra null is not to be treated as a value but merely a marker of unknown (absence of a value).

None of this is rocket science and I suggest doesn't result in bad implications. I suggest the so called "bad implications" are only introduced as people use null as a patch for problems for example the division by zero. indeterminate state, open ended ranges, data states to name a few. That is, the issue is not the concept of null but its abuse as a patch for other issues.


Why shouldn't we allow NULLs?,

3. An ONLINE exchange I participated in.

NULL Handling in Databases,

4. And now for something completely different.

An astonishing act of statistical chutzpah
Why Great Teachers Are Fleeing the Profession
The ABCs of MOOCs

What does this say about the educational system?

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