Towards Passive RFID Event

Passive RFID event refers to one kind of composite event in RFID middleware, one or more constituent sub-events of which do not occur under certain condition. Definition of passive RFID event requires careful consideration of temporal constraint and composition hierarchy, and moreover, the detection requires well-organized query plan for eventpsilas absence in runtime context. To process complex RFID business logic, we should be able to define a wide variety of passive event types with rigorous semantics as well as to perform efficient event detection. In this paper, we first demonstrate some logic difficulties and language expressiveness-related issues met by passive event definition. Then we design a RFID event definition language which especially well supports specifying complex hierarchical passive event with formal semantics. We also propose a Petri net-based event detection algorithm with a suit of optimization techniques for recognizing passive event. We finally compare our work with Espier in both language expressiveness and detection performance.