This paper describes a methodology and a framework For building an analyzable real-time model of an object-oriented system that is developed using UML CASE too. The real-time models is formulated by a new UML view named "MAST_RT_View". This view allows the designer to gradually build the real-time model according to the phase of the development process, to feed data into the analysis tools, and to bring the relevant timing response back into the model. The MAST_RT_View has three models: The processing capacity of the hardware/ software platform; the timing behavior of the application logical components; and the workload and the timing requirement of each real-time situation to be analyzed. This view is analyzable by the MAST set of tools, which Includes worst-case schedulability analysis and discrete-event simulation for hard and soft timing requirements.