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This paper describes a framework of a Web-based distributed control system (WBDCS) and the design and implementation of its software using a multitier client/server architecture and distributed object technology. The main issues addressed in this paper are the infrastructure of the system, the functionality of the components, and the real-time scheduling behavior of the application. CORBA is adopted to facilitate the communication between distributed objects across the Internet/intranet. Connectivity and controllability of on-line devices and their interaction with users are described. Because of the importance of timeliness in real-time systems, emphasis is put on time and event scheduling in the system. WBDCS features downloadable graphical user interfaces that display real-time status and process data of remote devices, allow an authorized user to access process variables and modify device configurations remotely. Built-in JNI ensures that customized control applications can be integrated into the distributed system. The programmable and reconfigurable framework of the system provides a flexible mechanism for constructing distributed real-time applications.