Complex Event Query Based On Regular Tree Pattern

With the rapid development of the Internet technology,more and more information is transmitted and shared over the network.Data of real-time systems usually arrives in real-time,such as the data provided by stock markets and social media sites.Correspondingly,demand for querying streaming data is increasing.Therefore,how to conduct a complex query efficiently on streaming data has become a problem eagerly to be tackled.In many fields,the event-response mechanism is often used as a computational model in information processing system,making the streaming data abstracted as a complex event stream,in which each query is mixed with constraints in both structure and time series.Complex event query is to retrieve data compliant with specific data model in line from the data stream.Consequently,how to achieve more power in event description and more efficiency in query processing have become two important research directions.Recently,XML has become a standard language for the exchange and storage of semi-structured data.Besides,Twig pattern query is the core of querying XML data.It can describe the structural constraints in XML query and achieve high efficiency with a holistic matching method.However,Twig pattern cannot describe the temporal constraints in complex event queries.In order to improve the descriptive ability of tree patterns,some operators in richer semantics are introduced into query requests,like the kliine-closure operator,the join operator,and more complex axis.Since the regular expression can describe the temporal constraints in complex event queries,we can add regular expressions into Twig pattern to form a regular tree pattern to describe much more complex events than usual.At present,the query methods for complex event mainly focus on the requests containing only structural constraints,regardless of the requests containing both structural and temporal constraints.With such concerns,this paper proposes an extended pattern-matching algorithm to efficiently process complex event queries by using a holistic matching method over XML streaming data based on the pushdown automata.This method can process the request containing both structural and temporal constraints as described in regular tree pattern.Our extensive experiments verify the efficiency and effectiveness of our approach.