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E. F. Codd believed in having (at least) two special values in a relational model: one to signify an inapplicable column, and another to represent an unknown va
by oftenwrong 9y ago
E. F. Codd believed in having (at least) two special values in a relational model: one to signify an inapplicable column, and another to represent an unknown value.
For example, if you had a "person" table, the "name" column could be INAPPLICABLE if the person does not have a name, and UNKNOWN if the person's name is not known.