The logic that underpins the relational model is a two-valuedlogic (2VL). SQL, specifically SQL's support for "nulls", is based on a three-valued logic (3VL) instead of the two valuedlogic (2VL). This logic attempts to address the "missinginformation" problem. This session explains why such an approach is doomed. It explains why 3VL (a), doesn't solve the problem, (b), isn't helpful, and (c), can be dangerous.
The presentation is divided into three parts. Module I reviews conventional two-valuedlogic (2VL), examines the most immediate differences between it (3VL),and shows how 3VL invariably leads to errors. Module II explains why such errors are inevitable. It also addresses the question: What 3VL are you referring to? Module III discusses many-valued logics, in general, and four valued logic (4VL), and also discusses a number of relatedpoints. It also briefly discusses a method of missinginformation that is based on classical relational theory and 2VL.
