Re: WWW/Internet 2009: 2nd CFP until 21 September
Date: Sun, 16 Aug 2009 20:04:36 GMT
Walter Mitty wrote:
> "paul c" <toledobythesea_at_oohay.ac> wrote in message
>> Mr. Scott wrote: >> ... >>> Pardon the pun, but your argument appears to be more applicable to >>> inapplicable nulls. ... >> Oh, here we go again, more twists and turns. I think Darwen said the >> record for the number of different kinds of nulls was somewhere in the >> twenties. >> >>
> This is one of the more screwy discussions among theoreticians. You have to
> draw a difference between indication and inference.
> The only thing that a null INDICATES is that data is missing. The reason
> why data is missing is either INFERENCE on the part of the reader, or else
> it's an out of band message (a metamessage) between the writer and the
> There are only two cases that I think are worth distinguishing. The first
> is, I guess, the inapplicasble null. This one arises from the fact that the
> number of cells in a table is constrained to be the product of the number of
> rows and the number of columns, but the number of placeholders needed might
> be less than that. This case can be obviated by normalization. I'm perhaps
> in the minority in c.d.t. in saying that there are cases where a design
> that's less than fully normalized can be a good one.
> The other case worth mentioning is that things are not what they should be.
> If there's any comprehensive theory on things that get screwed up, I'm
> unaware of it. Maybe the famous Murphy, of Murphy's law, created such a
> theory. Theory or no, people whio build systems in the real world try to
> build systems retain some of their value when things get screwed up.
Somewhere Date gives a nice little example of the pitfalls when trying to record negative facts. Some predicates can be very tricky. One analogy I like has to do with troubleshooting motorcycle charging and electrical systems. Ususually the prescribed tests for parts like coils and rectifiers involve an electrical continuity test. These tests will tell you if a part is definitely bad, but they won't tell you if it's definitely good! So you can't negate that kind of predicate. Received on Sun Aug 16 2009 - 22:04:36 CEST