As the Web of Data grows, the number of available SPARQL endpoints increases. SPARQL endpoints conceptually represent RPC-style, coarse-grained data access mechanisms. Nevertheless, through the potential interlinking ...As the Web of Data grows, the number of available SPARQL endpoints increases. SPARQL endpoints conceptually represent RPC-style, coarse-grained data access mechanisms. Nevertheless, through the potential interlinking of the contained entities, SPARQL endpoints should be able to over distinct advantages over plain Web APIs. To our knowledge, to date, there has been no study conducted that gauges the impact of the link on SPARQL query execution, especially in a federated set-up. In this paper, we investigate how the existence and types of typed links influences the execution characteristics of different SPARQL federation frameworks. In order to measure the query performance, we propose a combined cost model based on a statistic analysis of the query performance metrics that involves parameters such as type of link, the data catalogues and cache, number of links, and number of distinct subjects. As result, we show that number of distinct subject and number of links have significant impact on Federation over SPARQL Endpoints performance whereas type of link does not have significantly influence in federation query performance.展开更多
Congestion in wireless sensor networks (WSNs) not only causes severe information loss but also leads to excessive energy consumption. To address this problem, a novel scheme for congestion avoidance, detection and all...Congestion in wireless sensor networks (WSNs) not only causes severe information loss but also leads to excessive energy consumption. To address this problem, a novel scheme for congestion avoidance, detection and alleviation (CADA) in WSNs is proposed in this paper. By exploiting data characteristics, a small number of representative nodes are chosen from those in the event area as data sources, so that the source traffic can be suppressed proactively to avoid potential congestion. Once congestion occurs inevitably due to traffic mergence, it will be detected in a timely way by the hotspot node based on a combination of buffer occupancy and channel utilization. Congestion is then alleviated reactively by either dynamic traffic multiplexing or source rate regulation in accordance with the specific hotspot scenarios. Extensive simulation results under typical congestion scenarios are presented to illuminate the distinguished performance of the proposed scheme.展开更多
文摘As the Web of Data grows, the number of available SPARQL endpoints increases. SPARQL endpoints conceptually represent RPC-style, coarse-grained data access mechanisms. Nevertheless, through the potential interlinking of the contained entities, SPARQL endpoints should be able to over distinct advantages over plain Web APIs. To our knowledge, to date, there has been no study conducted that gauges the impact of the link on SPARQL query execution, especially in a federated set-up. In this paper, we investigate how the existence and types of typed links influences the execution characteristics of different SPARQL federation frameworks. In order to measure the query performance, we propose a combined cost model based on a statistic analysis of the query performance metrics that involves parameters such as type of link, the data catalogues and cache, number of links, and number of distinct subjects. As result, we show that number of distinct subject and number of links have significant impact on Federation over SPARQL Endpoints performance whereas type of link does not have significantly influence in federation query performance.
基金Project supported by the National Natural Science Foundation of China (Nos. 60673180, 90412011 and 90612004)the International Science and Technology Cooperative Program of China (No. 2006DFA11080)+1 种基金the Research Program of Federal Ministry of Education and Research of Germany (No. 01BU0680)the Lion Project of Science Foundation of Ireland to Lei Shu (No. SFI/08/CE/ I1380)
文摘Congestion in wireless sensor networks (WSNs) not only causes severe information loss but also leads to excessive energy consumption. To address this problem, a novel scheme for congestion avoidance, detection and alleviation (CADA) in WSNs is proposed in this paper. By exploiting data characteristics, a small number of representative nodes are chosen from those in the event area as data sources, so that the source traffic can be suppressed proactively to avoid potential congestion. Once congestion occurs inevitably due to traffic mergence, it will be detected in a timely way by the hotspot node based on a combination of buffer occupancy and channel utilization. Congestion is then alleviated reactively by either dynamic traffic multiplexing or source rate regulation in accordance with the specific hotspot scenarios. Extensive simulation results under typical congestion scenarios are presented to illuminate the distinguished performance of the proposed scheme.
