Note from the author: Much of the text in this appendix was originally part of Chapter 3—the last chapter that Lex had been able to spend time on at the end of 2005. Being called “Mr. NULL,” as some of you might know, he produced quite a bit of text on the topic of NULLs and 3-valued logic (3VL) as part of Chapter 3. By the time Chapter 3 review comments were in and I (Toon) started working on them, I decided that it would be better, for Chapter 3, to move all text with regards to NULLs and 3VL out of Chapter 3 and into this appendix.

During his career, my coauthor dedicated quite a bit of time to investigating the phenomenon of a NULL “value” ...

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