Keys and foreign keys play a crucial role in relational databases-keys identify the objects of interest, and foreign keys knit those objects together. The basic idea couldn't be simpler. As so often, however, the devil is in the detail ... The fact is, these concepts aren't quite as straightforward as they might seem on first acquaintance-or, at least, such would appear to be the case, if the literature is anything to go by. In this one of a kind book, noted database author C. J. Date traces the somewhat checkered history of the key and foreign key concepts, shedding some light on what turns out to be, on occasion, a surprisingly murky subject and explaining in detail what proper support should look like in true relational products. Topics covered include a detailed look at the pertinent theory; a critical review of the historical development of these ideas; and a couple of important case studies, one having to do with the SQL standard and one with the IBM DB2 product family. No serious database professional can afford to be without this book.