Dynamic evolution is an important phenomenon in distributed systems that undergo changes without being shut down. Examples include 24x7 global financial market systems and mobile phone switching networks. Building and keeping these systems operational requires sound software engineering techniques since system unavailability is extremely expensive and is often prohibited in many business contexts. In this spirit, we present temporal extensions to the UML notation to incorporate design concerns for dynamic evolution in distributed system development. In the system structure space, this paper introduces the temporal system structure, the transformational association, the transformational link, and the state transfer map to relate successive changes to each other. In the transformation space, this paper introduces the use of exclusion control to regulate and maintain service continuity during a transformation, and the transformation diagram to specify a transformation per se with respect to time.