Extending the Database Relational Model to Capture More Meaning¶
Codd, E. F. (1979). Extending the Database Relational Model to Capture More Meaning. ACM Transactions on Database Systems, 4(4), 397-434.
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- Its treatment of the three empties is really an application of null semantics — the discipline, familiar from SQL's three-valued logic, of distinguishing "absent/unknown" from "known to be empty," because conflating them silently corrupts every count downstream.
This sourceIntroduces three-valued database logic in which comparisons involving null values can evaluate to unknown rather than true or false.
- Its treatment of the three empties is really an application of null semantics — the discipline, familiar from SQL's three-valued logic, of distinguishing "absent/unknown" from "known to be empty," because conflating them silently corrupts every count downstream.
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