The first edition of this book appeared in 1998, at which point the Unified Modeling Language, UML, was beginning to be widely adopted. Since then, it has become the dominant software modeling language, widely used and taught. UML underwent several minor revisions. Over the last several years, the Object Management Group (OMG) has been working on the first major revision of UML, now released as UML2.0. This makes many significant changes to the language, whilst leaving the core of the notation intact.