| As object-oriented(OO) technique has been widely used in the design and construction of software systems, People begin to use Object-oriented technique to design and analyse embedded real-time system. Through the process of object-oriented designing and anlysing, developers often use Model to help them to achieve their goal. In real-time system, there are many activity which is running concurrently. This activity is finally implemented by process which form the basic concurrent running unit in the final exetable system. As the standard modeling language, UML is the most important achievement in the object-oriented technique. During the developing of system based on UML, developers used to using active object to represent the concurrent entity. Because the shortage of the describing capability, active object often fail to describe the system concurrency explicitly. So it is necessary to introduce a new method and a new mechanism to describe real-tme concurrency.In this paper, we introduce a new modeling method which is base on some new model element according to the real-time system charactetistic. This element which is base on UML extension mechanism is a complementary of UML standard semantic. Firstly ,we define the UML semantic of this model element based on UML extension mechanism, including capsule that is a kind of active class to represent the concurrent unit and protocol derived from collaboration, which mainly is used to describe the communication between capsules. Secondly, we introduce how to modeling the real-time system using this element based on UML standard modeling mechanism. Finaly, we provide a proposal of constructing foundation class libration of C++ according to semantic of capsule and protocol, as well as the method to construct the domain class derived from the foundation class. It enable us to construct a formal model for real-time system concurrency which is the foundation of generation of code and also to validate system by formal analyse method.
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