构建结果子树是XML关键字查询处理的核心问题,其中求解与每个子树根节点相关的关键字节点是影响结果子树构建效率的重要步骤。针对已有方法不能正确求解基于ELCA(exclusive lowest common ancestor)语义的相关关键字节点(RKN,relevant k...构建结果子树是XML关键字查询处理的核心问题,其中求解与每个子树根节点相关的关键字节点是影响结果子树构建效率的重要步骤。针对已有方法不能正确求解基于ELCA(exclusive lowest common ancestor)语义的相关关键字节点(RKN,relevant keyword node)的问题,提出RKN的形式化定义及相应的RKN-Base算法。该算法通过顺序扫描每个关键字节点一次即可正确判断其是否为某个ELCA节点的RKN。针对RKN-Base不能避免处理无用节点的问题,提出一种优化算法RKN-Optimized,该算法基于每个ELCA节点求其RKN集合,从而避免了对无用节点的处理,降低了时间复杂度。最后,通过实验验证了所提算法的高效性。展开更多
In this paper, we focus on efficient construction of restricted subtree （RSubtree） results for XML keyword queries on a multicore system. We firstly show that the perfor- mance bottlenecks for existing methods lie i...In this paper, we focus on efficient construction of restricted subtree （RSubtree） results for XML keyword queries on a multicore system. We firstly show that the perfor- mance bottlenecks for existing methods lie in 1） computing the set of relevant keyword nodes （RKNs） for each subtree root node, 2） constructing the corresponding RSubtree, and 3） parallel execution. We then propose a two-step generic top-down subtree construction algorithm, which computes SLCA/ELCA nodes in the first step, and parallelly gets RKNs and generates RSubtree results in the second step, where generic means that 1） our method can be used to compute dif- ferent kinds of subtree results, 2） our method is independent of the query semantics; top-down means that our method con- structs each RSubtree by visiting nodes of the subtree con- structed based on an RKN set level-by-level from left to right, such that to avoid visiting as many useless nodes as possible. The experimental results show that our method is much more efficient than existing ones according to various metrics.展开更多
An exergy life cycle assessment(ELCA) model based on life cycle assessment(LCA) and exergy methodology was developed to assess a 2×300 MW coal-fired power plant,and the results indicated that the exergy input in ...An exergy life cycle assessment(ELCA) model based on life cycle assessment(LCA) and exergy methodology was developed to assess a 2×300 MW coal-fired power plant,and the results indicated that the exergy input in operation phase of power plant accounts for 99.89% of the total input and only 0.11% in construction and decommission phases. Direct and indirect exergy inputs account for 93.03% and 6.97%,respectively. Compared with coal-fired power generation system before carbon emission reduction,exergy input-output ratio of life cycle "CO2 zero-emission" energy system and exergy efficiency are about 5.563 and 17.97%,respectively,which increases by 62.47% and declines by 11.21% approximately. The model quantifies the energy,resource consumption and pollutant emissions of system life cycle using exergy as the basic physical parameter,which will make the assessment more objective and reasonable.展开更多
基金This work was partially supported by the National Natural Science Foundation of China （Grant Nos. 61272124, 61103139, 61472339 and 61303040）.
文摘In this paper, we focus on efficient construction of restricted subtree （RSubtree） results for XML keyword queries on a multicore system. We firstly show that the perfor- mance bottlenecks for existing methods lie in 1） computing the set of relevant keyword nodes （RKNs） for each subtree root node, 2） constructing the corresponding RSubtree, and 3） parallel execution. We then propose a two-step generic top-down subtree construction algorithm, which computes SLCA/ELCA nodes in the first step, and parallelly gets RKNs and generates RSubtree results in the second step, where generic means that 1） our method can be used to compute dif- ferent kinds of subtree results, 2） our method is independent of the query semantics; top-down means that our method con- structs each RSubtree by visiting nodes of the subtree con- structed based on an RKN set level-by-level from left to right, such that to avoid visiting as many useless nodes as possible. The experimental results show that our method is much more efficient than existing ones according to various metrics.
基金supported by the National Natural Science Foundation of China (Grant Nos.40972102,50936001,51021065)the National Basic Research Program of China ("973" Project) (Grant No.2010CB227003)
文摘An exergy life cycle assessment(ELCA) model based on life cycle assessment(LCA) and exergy methodology was developed to assess a 2×300 MW coal-fired power plant,and the results indicated that the exergy input in operation phase of power plant accounts for 99.89% of the total input and only 0.11% in construction and decommission phases. Direct and indirect exergy inputs account for 93.03% and 6.97%,respectively. Compared with coal-fired power generation system before carbon emission reduction,exergy input-output ratio of life cycle "CO2 zero-emission" energy system and exergy efficiency are about 5.563 and 17.97%,respectively,which increases by 62.47% and declines by 11.21% approximately. The model quantifies the energy,resource consumption and pollutant emissions of system life cycle using exergy as the basic physical parameter,which will make the assessment more objective and reasonable.
