An effective way to optimize XML queries is to minimize XML queries. In this paper, we improve redundance elimination in XPath queries greatly by incorporating two novel kinds of constraints: parent constraint and sib...
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An effective way to optimize XML queries is to minimize XML queries. In this paper, we improve redundance elimination in XPath queries greatly by incorporating two novel kinds of constraints: parent constraint and sibling constraint, and by extending the tractable fragment to include descendant-or-self axis. The two novel kinds of constraints, together with child constraint and descendant constraint, form a family of constraints, which complicate the problem but offer possibilities for further minimization. Two techniques, tree augmentation and simulation augmentation, are employed to cope with constraints. We elaborate on the minimizing algorithms and running efficiencies both in the absence and in the presence of various kinds of constraints.
Recent advances in database related applications propose many new challenges and have inspired database researchers and practitioners to further make their efforts on new database technologies.
Recent advances in database related applications propose many new challenges and have inspired database researchers and practitioners to further make their efforts on new database technologies.
作者：
王珊杜小勇孟小峰陈红School of Information
Renmin University of China MOE Key Lab of Data Engineering and Knowledge Engineering Beijing 100872 P.R. China
database system is the infrastructure of the modern information system. The R＆D in the database system and its technologies is one of the important research topics in the field. The database R＆D in China took off la...
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database system is the infrastructure of the modern information system. The R＆D in the database system and its technologies is one of the important research topics in the field. The database R＆D in China took off later but it moves along by giant steps. This report presents the achievements Renmin University of China （RUC） has made in the past 25 years and at the same time addresses some of the research projects we, RUC, are currently working on. The National Natural Science Foundation of China supports and initiates most of our research projects and these successfully conducted projects have produced fruitful results.
Poyang Lake watershed mainly consists of Poyang Lake and its five sub-watersheds. Its wetlands, the largest bird habitat in Asia, play an important role in biodiversity and ecologic protection. With the rapid economic...
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ISBN:
(纸本)1892769530
Poyang Lake watershed mainly consists of Poyang Lake and its five sub-watersheds. Its wetlands, the largest bird habitat in Asia, play an important role in biodiversity and ecologic protection. With the rapid economic growth and urbanization, the wetlands in Poyang Lake area have been shrinking and face many environmental challenges. To better understand the environmental and ecologic changes of wetlands in the Poyang Lake watersheds, we applied RS/GIS techniques and a mathematical model in a study of the relationship between land use/cover changes and sediment load of the Poyang Lake watershed. RS classification was used to detect the land use/cover change, and a relational searching algorithm of spatial objects was proposed to improve the classification accuracy of wetlands. The driving forces for the land use/cover change were also analyzed. Soil erosion by water, as a big environmental problem, reflects the process of surface water related to non - point source pollution that influences water quality, the environment, and ecology of wetlands. In this study GIS and RS technologies are employed to predict annual soil loss. This work prioritizes erosion-prone areas which are important sources of sediment and highlights the severity of soil erosion in the watershed. SSC (suspended sediment concentration) data were collected for the study period. The relationships among land use/cover change, erosion area variations and SSC alterations are examined for the study period. The results show that the land use/cover change in the watershed lessen sediment sources and led to less SSC load to the wetland. The Poyang Lake is less impacted by the SSC in 2000 compared with 1991.
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