I'm sorry to have to say this, but this is the worst technical book I've ever read. I expected much more from O'Reilly than this. The examples given are incomprehensible and badly organized. Not only are the example diagrams poor in details, but the author mixes themes from one example to the next, thus breaking any consistency in his explanations. The text is unnecessarily difficult to read. Key words and terms specific to UML are either poorly defined or not defined at all, making nearly every sentence in the book a chore to understand. I find that even my simplest questions go unanswered in both the text and the examples. To make matters worse, the chapters and subsections are so vague that I can't refer back to points that I remembered reading about to get clarification without re-reading entire chapters. This is one of those rare books that is useless both for serious study and as a reference.
"UML 2.0 In a Nutshell", c. 2005 by O'Reilly Media, Dan Pilone