기술개요
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Most previous research efforts for continuous query processing use a tree-structured execution plan employed in a conventional database management system in order to determine the execution order of binary join operations specified in a query. However, the selectivity of a join operation over infinite data streams is mostly unpredictable, so that they require to perform adaptive query re-optimization which causes a serious run-time burden. To eliminate the need of adaptive query re-optimization, this paper proposes a new evaluation framework called 2-phase evaluation scheme (2PE) for a multi-way join query. The first phase examines the satisfiability of each source tuple of a data stream for a given query. Based on this information, the second phase materializes the final result tuples of the query explicitly without generating any unsatisfiable intermediate tuple. Accordingly, a continuous query that only detects the invocation of a particular event can be answered by the first phase only.
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