The Unified Modeling Language (UML) is a standardized general-purpose modeling language used to specify, document, and visualize software systems. The UML includes a set of well-defined and expressive notations used to create visual models of software systems. This standard set of notation makes it possible for an architecture to be formulated and communicated unambiguously to others. Since the Object Management Group (OMG), an international notfor-profit consortium that creates ards for the computer industry, adopted the UML as a standard in 1997, the UML has been revised many times. In this chapter, we give a brief introduction to UML 2.0. For further details on UML 2.0, readers are referred to Booch et al. (2007). In what follows, UML means UML 2.0.