Small Wonder

Programmers have a lot of trouble with the concept of null, as found in relational databases.

There's a good reason for that. In regular boolean logic, there are 16 binary operators - the usual suspects like AND, OR, XOR, and implication and its converse; their negations; and the six degenerate forms that aren't truly binary at all - P, Q, their negations, and T and F (tautology and contradiction).

Okay?

There are 256 ternary boolean operators, as any hardcore Amiga programmer would know. (The Amiga's blitter allowed you to process three image sources into a destination, and you could program it to perform any one of the 256 possible operators.)

If you throw in null, so that you have three-valued, or ternary, logic, you now have 19,683 binary operators. (That is, binary ternary operators.  And 7,625,597,484,987 ternary ternary operators, which is why no-one made a three-valued Amiga.)

In 1990, Codd suggested that four-valued rather than three-valued logic was better for the relational model, dividing the concept of null into Missing but Applicable (A-values) and Missing but Inapplicable (I-values). I call them don't know and don't care, or none and any. (Because if you don't know and it matters, no value will give you the right answer, while if you don't care, any value will do.)

This does give you a more precise way of handling missing data. It also gives you 4,294,967,296 binary operators. That's probably why it hasn't really caught on yet.

Posted by: Pixy Misa at 12:30 AM | Comments (3) | Add Comment | Trackbacks (Suck)
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