Table of Contents Introduction 1. “Inapplicable Data”: Nothing's Missing 2. Missing Data: Into the Unknown 3. SQL NULL: What-Valued Logic? 4. Known Unknowns: Metadata 5. A Relational Solution 5.1. The Practicality of Theory 5.2. A Real World Example 5.3. Relation Proliferation 6. Questions/Comments/Objections Conclusion