Model of Execution Center in Multi-Task CAD Systems

We present the Event-Driven Hierarchy model （EDHM） of execution center，aiming at fulfilling the requirements of direct-manipulation such as real-time feedback and concurrent di-alog in multi-task CAD systems．The EDHM model conforms to the principle of independence for human-computer interaction，divides the execution center into three levels and five modules．It supports continuous semantic feedback and asynchronous concurrent interaction，provides the mixed styles of interaction in a uniform framework．This model has been applied to the construction of execution center of OpenDesign （a CAD supporting system） and is proved to be a solid base for the modeling and implementation of efficient execution centers that support direct manipulation and multi-process．In addition，execution center based on EDHM model is independent in structure，thus is easy to port and reuse．