T u t o r i a l D (version dated May 23rd, 2013, superseding all previous versions) I never use a big, big D— —W. S. Gilbert: HMS Pinafore The version immediately preceding this one is Chapter 11 in Database Explorations by C. J. Date and Hugh Darwen, Trafford, 2010. What follows is a revision of the body of that chapter, with altered and new text shown in blue. On October 30th, 2011, the Boolean operator EQUIV was added (see the section SCALAR DEFINITIONS and
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