Research On An Approach Of Multi-queries Sharing Over RFID Event Streams

RFID (Radio Frequency Identification) technology is a new information technology, which is widely used in many fields, such as military, physical distribution, security check. However there are many challenges in processing the RFID event stream. In many aspects, lots of technologies need to be improved; in particular the query over RFID event streams becomes the hot and difficult. Queries over RFID event streams are mainly continuous queries. These queries are constituted by specific basic events according to a certain logical operation. These queries are executed to detect composite events over basic event streams(formed by cleaning the original reading from readers). Composite event queries are often referred to as composite event detection. There are hundreds of compsite event queries over basic events streams for a period of time. These queries are all residing in RFID system at the same time, in order to improve the efficiency of the system, it's necessary to share between multiple continuous queries.Currently studies of RFID event streams mainly concentrate on the cleaning of the primitive event streams, the non-deterministic approach and the effective implementation of a single composite event query, while studies involved in the effective implementation of multi-composite event queries are less. In this paper, we study further about the multi-composite event query sharing over RFID event streams, aiming at the weaknesses of existing approaches, we propose an approach of the multi-composite event queries sharing based on small event, specific working is as follows:Aiming at the storage problem of sharing multiple queries, this paper proposes the structure of composite event graph as internal representation of the query. Then, aiming at the problem of sharing the sub-queries which have different operators, and the same associated operand, we propose the concept of small event by analyzing the semantics of composite events and the relationship between operators, gived rules and properties of the query rewriting. We can rewrite all queries to disjunctive normal form of small events by following the rules and properties, to seek a wider rang of the sub-query sharing. Finally, a sharing mechanism of composite event queries based on small event is proposed. It gives methods of small event sharing and complex small events to achieve the further sharing of composite event queries, gives the solving approach of the largest share of small event and complex small event, gives a method of combining multiple graphs of composite event and the node structure, and gives the algorithm of the query sharing based on small event. So as to improve the query efficiency of the overall system, meet the requirements of the real-time and online query.By comparing the memory utilization and detection efficiency between the shared RFID composite event query algorithm and RCEDA, show that the paper proposed method of multi-queries sharing is higher, especially when the number of queries significantly increased, the efficiency is more evident.