Preface

I've been lucky in a lot of ways in my life; one of my great strokes of fortune was being in the right place with the right knowledge to write the first edition of this book in 1997. Back then, the chaotic world of object-oriented (OO) modeling was just beginning to unify under the Unified Modeling Language (UML). Since then, the UML has become the standard for the graphical modeling of software, not just for objects. My fortune is that this book has been the most popular book on the UML, selling more than a quarter of a million copies.

Well, that's very nice for me, but should you buy this book?

I like to stress that this is a brief book. It's not intended to give you the details on every facet of the UML, which has grown and grown over the years. My intention is to find that fraction of the UML that is most useful and tell you just that. Although a bigger book gives you more detail, it also takes longer to read. And your time is the biggest investment you'll make in a book. By keeping this book small, I've spent the time selecting the best bits to save you from having to do that selection yourself. (Sadly, being smaller doesn't mean proportionately cheaper; there is a certain fixed cost to producing a quality technical book.)

One reason to have this book is to begin to learn about the UML. Because this is a short book, it will quickly get you up to speed on the essentials of the UML. With that under your belt, you can go into more detail on the UML with the bigger books, such as the User Guide [Booch, UML user] or the Reference Manual [Rumbaugh, UML Reference].

This book can also act as a handy reference to the most common parts of the UML. Although the book doesn't cover everything, it's a lot lighter to carry around than most other UML books.

It's also an opinionated book. I've been working with objects for a long time now, and I have definite ideas about what works and what doesn't. Any book reflects the opinions of the author, and I don't try to hide mine. So if you're looking for something that has a flavor of objectivity, you might want to try something else.

Although many people have told me that this book is a good introduction to objects, I didn't write it with that in mind. If you are after an introduction to OO design, I suggest Craig Larman's book [Larman].

Many people who are interested in the UML are using tools. This book concentrates on the standard and on conventional usage of the UML and doesn't get into the details of what various tools support. Although the UML did resolve the tower of Babel of pre-UML notations, many annoying differences remain between what tools show and allow when drawing UML diagrams.

I don't say much in this book about Model Driven Architecture (MDA). Although many people consider the two to be the same thing, many developers use the UML without being interested in MDA. If you want to learn more about MDA, I would start with this book to get an overview of the UML first and then move on to a book that's more specific about MDA.

Although the main point of this book is the UML, I've also added bits of other material about techniques, such as CRC cards, that are valuable for OO design. The UML is just a part of what you need to succeed with objects, and I think that it's important to introduce you to some other techniques.

In a brief book like this, it's impossible to go into detail about how the UML relates to source code, particularly as there is no standard way of making that correspondence. However, I do point out common coding techniques for implementing pieces of the UML. My code examples are in Java and C#, as I've found that these languages are usually the most widely understood. Don't assume that I prefer those languages; I've done too much Smalltalk for that!