This is a useful reference to the Unified Modelling Language.
To start with, this book is fairly compact meaning that it wont take up much space on your bookshelf and can be easily carried around with you allowing you to work on your design in spare moments when you are away from your computer. Despite its small size the book is a convenient reference to UML since it has separate chapters covering each of the major diagram types. The book also has lots of diagrams that show you how UML works rather than your just reading about it. The authors have written the book from (in their own words) a "why you might care" perspective which means that while they cover all aspects of UML they spend the most time on those diagrams that are most likely to be useful in designing a computer system.
The book makes no assumptions about the reader's knowledge of UML. Each chapter begins with a top-to-bottom discussion of the chapter's contents, offering plenty of examples and discussions of how UML can be applied. The book has been written primarily as a reference so it may not be the best choice of book if you are just starting out learning UML (particularly if you have no prior knowledge of Object Oriented Design) but provided that you have some exposure to UML you will be able to easily work out the less diagrams should you find a use for them using the information provided in this book.