Re: NULLs: theoretical problems?

From: David Cressey <>
Date: Sat, 11 Aug 2007 11:09:13 GMT
Message-ID: <tNgvi.37$tU4.25_at_trndny03>

"Hugo Kornelis" <> wrote in message
> Let me put it in another way. The presence of ANY value in a database,
> not just NULL, implies two facts. One is the recorded fact - eg an 'N'
> in the "HasKids" column implies that the respondent does not have kids.
> But there's another fact implied as well, one that is usually not
> recorded - to wit, the reason why there's an 'N' there. Was it entered
> by the interviewer after asking the interviewed person if she has kids?
> Did the interviewer check the interviewed's house for toys, just to be
> sure, or did he believe the answer? Was there an interviewer involved at
> all, or was this 'N' filled out in a web form? If so, could it be the
> case that the respondent thought entering 'N' meant "No, I don't want to
> share this information"? Or that her native tongue has a word starting
> with 'N' that means "Yes"? Heck, maybe she wanted to enter 'Nine' and
> never noticed that only a single character was accepted!
> Okay, the last examples are a bit over the top, but I think you do get
> my point: for EVERY value in a database, you can ask the question what
> this actually means and why that value is there. We just don't usually
> do it - except when that value is not a value at all, but rather a
> symbol to denote the absence of a value.


The data that explains why other data is (or is not) recorded is really data about data, not data about the subject matter. Data about data has a name: metadata. We are accustomed to thinking of metadata as defining theother data it talks about. I guess it can also act as an "apology" for that data (or its absence) as well. Received on Sat Aug 11 2007 - 13:09:13 CEST

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