UML 2 represents the most significant overhaul to UML since it was first agreed upon. One thing hasn’t changed, though: UML Distilled is the place to begin.

Over the years, Martin Fowler’s short book has collected raves from folks who know...folks like Jim Rumbaugh and Stephen J. Mellor. It’s just so accessible, clear, realistic — and so well-focused on the essence of UML. This edition’s no exception.

Many folks treat UML as a tool for informal, collaborative “sketching”: roughing out issues and alternatives or clarifying a legacy system’s behavior. This may be the only UML book they’ll ever need. Others use it to build exhaustive blueprints for coding. Some are even trying to compile UML diagrams directly to executable code: The UML is the source. Blueprinters and “executable XML” types will eventually need to go beyond this book’s 170 pages, but Fowler does a superb job of getting them started.

After a thoughtful essay on integrating UML into your workflow, he introduces each “official” UML diagram type. He begins with class diagrams — from the basics through advanced topics such as parameterization. There’s a solid introduction to use cases: the diagrams, when to use them, and how they relate to features and “user stories.” There’s expert coverage of state machine diagrams, from internal activities to concurrent states.

Among the many UML 2 updates: a new chapter on composite structures for describing classes hierarchically (very helpful in managing complexity). There’s also far more coverage of activity diagrams, which have been extensively enhanced to permit the modeling of complex processes. If you’re new to UML, you’ll admire this slim volume.