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NULL, N.A., Undefined, Unknown values

Jean Richelle (jean@ucmb.ulb.ac.be)
Thu, 19 Jan 1995 16:28:42 +0100 (MET) 

Hello,

This question is directed specifically to John Westbrook but others may 
have enlignments on the subject.

I wonder how it is possible to specify NULL, N.A. (Not Applicable), 
Undefined, Unknown values for data items of any types. I don't remember 
nothing regarding this in the DDL.

Jean