Recently, many global enterprises build an RFID system for their RTE environments. In an RFID system, it is necessary to provide the RFID middleware managing RFID tag information captured by multiple RFID readers efficiently. RFID middleware systems should provide transparency for RFID data streams by heterogeneous readers and high performance for processing queries in real-time. They should also support new readers easily and accept large number of readers and queries. In this paper, we analyze requirements in order to process RFID data streams efficiently in the RFID middleware. We classify the requirements into the abstraction, the high performance, the extensibility, the scalability and the availability. We also propose the architecture of the RFID middleware based on various methods to meet five requirements. Finally, we design and implement the RFID middleware architecture for providing efficient query processing on RFID data streams.