Hello Ed, (01)
On Tue, Jan 22, 2013 at 11:51:28AM -0500, Barkmeyer, Edward J wrote:
> At the risk of sounding like an old pedagogue, you might consider reading a
>Ted Codd paper from about 1980 on the possible interpretations of Null.
> My recollection is that he identified at least 4 possible interpretations:
> 1) No value is meaningful (the property does not apply to things with
>whatever other properties are documented)
> Example: a person whose marital status is "single" does not have a value
>for "spouse"
> 2) No value in this instance (the thing does not have an instance of this
>property)
> Example: a person may have no value for "mobile phone number" (by not
>having the service)
> 3) The value should exist but is not known (no one entered this datum)
> Example: a missing "date of birth"
> 4) Whether there is a value is unknown
> And there is a further state that we now sometimes see:
> 5) The value has been redacted. It may be in the database, but it is not
>in the query result, because the requester does not have the authority to ask
>for it (in this case).
>
> And there may well be others. "Null" is a Humpty Dumpty word. (02)
This Humpty Dumpty word seems to have a lot of use cases. Looks quite useful
to me (and has been in RDB projects). (03)
Do current RDBs actually behave differently regarding Null ? Otherwise I would
not see any problem. I don't care a bit about semantics as long as my tool has
a well defined behavior. (04)
Regards, (05)
Michael Brunnbauer (06)
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