垂直数据分区技术从逻辑上将满足一定语义条件的数据库表属性存放在同一个物理块中,进而降低数据访问成本,提高查询效率.数据库查询负载中的每条查询通常只与数据库表中的部分属性有关,因此只需使用数据库表的某个属性子集便可以得到准...垂直数据分区技术从逻辑上将满足一定语义条件的数据库表属性存放在同一个物理块中,进而降低数据访问成本,提高查询效率.数据库查询负载中的每条查询通常只与数据库表中的部分属性有关,因此只需使用数据库表的某个属性子集便可以得到准确的查询结果.合理的垂直数据分区方式可以使大多数查询负载不需要扫描完整数据库就可以完成查询任务,从而达到减少数据访问量,提高查询处理效率的目的.传统的数据库垂直分区方法主要基于专家设置的启发式规则,分区策略粒度较粗,且不能根据负载的特征进行有针对性的分区优化.同时,当负载规模较大或者属性个数较多时,现有垂直分区方法执行时间过长,尤其无法满足数据库在线实时调优的性能需求.为此,提出在线环境下基于谱聚类的垂直数据分区方法(spectral clustering based vertical partitioning,SCVP),采用分阶段求解的思想,减少算法时间复杂度,加快分区执行速度.首先通过增加约束条件缩小解空间(即根据谱聚类生成初始分区),然后对解空间设计算法进行精细的搜索(即采用频繁项集和贪心搜索相结合的策略对初始分区进行优化).为了进一步提升SCVP在高维属性下的性能,提出了SCVP的改进版本SCVP-R(spectral clustering based vertical partitioning redesign).SCVP-R通过引入同域竞争机制、双败淘汰机制和循环机制,对SCVP在分区优化过程中的合并方案进行了进一步优化.在不同数据集上的实验结果表明,相比于目前最好的垂直分区方法,SCVP和SCVP-R有着更快的执行时间和更好的性能表现.展开更多
This paper presents a collaborative 3D GIS to support public participation.Realizing that public-involved decision-making is often a multistage process,the proposed system is designed to provide coherent support for c...This paper presents a collaborative 3D GIS to support public participation.Realizing that public-involved decision-making is often a multistage process,the proposed system is designed to provide coherent support for collaborations in the different stages.We differentiate ubiquitous participation and intensive participation and identify their suitable application stages.The proposed system,then,supports both of the two types of participation by providing synchronous and asynchronous collabora-tion functionalities.Applying the concept of Digital Earth,the proposed system also features a virtual globe-based user interface.Such an interface integrates a variety of data,functions,and services into a unified virtual environment which is delivered to both experts and public participants through the Internet.The system has been designed as a general software framework and can be tailored for specific projects.In this study,we demonstrate it using a scene modeling case and provide a preliminary evaluation toward its usability.展开更多
文摘垂直数据分区技术从逻辑上将满足一定语义条件的数据库表属性存放在同一个物理块中,进而降低数据访问成本,提高查询效率.数据库查询负载中的每条查询通常只与数据库表中的部分属性有关,因此只需使用数据库表的某个属性子集便可以得到准确的查询结果.合理的垂直数据分区方式可以使大多数查询负载不需要扫描完整数据库就可以完成查询任务,从而达到减少数据访问量,提高查询处理效率的目的.传统的数据库垂直分区方法主要基于专家设置的启发式规则,分区策略粒度较粗,且不能根据负载的特征进行有针对性的分区优化.同时,当负载规模较大或者属性个数较多时,现有垂直分区方法执行时间过长,尤其无法满足数据库在线实时调优的性能需求.为此,提出在线环境下基于谱聚类的垂直数据分区方法(spectral clustering based vertical partitioning,SCVP),采用分阶段求解的思想,减少算法时间复杂度,加快分区执行速度.首先通过增加约束条件缩小解空间(即根据谱聚类生成初始分区),然后对解空间设计算法进行精细的搜索(即采用频繁项集和贪心搜索相结合的策略对初始分区进行优化).为了进一步提升SCVP在高维属性下的性能,提出了SCVP的改进版本SCVP-R(spectral clustering based vertical partitioning redesign).SCVP-R通过引入同域竞争机制、双败淘汰机制和循环机制,对SCVP在分区优化过程中的合并方案进行了进一步优化.在不同数据集上的实验结果表明,相比于目前最好的垂直分区方法,SCVP和SCVP-R有着更快的执行时间和更好的性能表现.
基金This work is supported by the National Natural Science Foundation of China[grant number 41001270]the Specialized Research Fund for the Doctoral Program of Higher Education[grant number 20100076120017]+2 种基金the Specialized Research Fund of Key Lab of Geographic Information Science,Ministry of Education[grant number KLGIS2011C04]the Grant from Shanghai Key Lab for Urban Ecological Processes and Eco-Restoration[grant number SHUES2012A03]the Fundamental Research Funds for the Central Universities of China.
文摘This paper presents a collaborative 3D GIS to support public participation.Realizing that public-involved decision-making is often a multistage process,the proposed system is designed to provide coherent support for collaborations in the different stages.We differentiate ubiquitous participation and intensive participation and identify their suitable application stages.The proposed system,then,supports both of the two types of participation by providing synchronous and asynchronous collabora-tion functionalities.Applying the concept of Digital Earth,the proposed system also features a virtual globe-based user interface.Such an interface integrates a variety of data,functions,and services into a unified virtual environment which is delivered to both experts and public participants through the Internet.The system has been designed as a general software framework and can be tailored for specific projects.In this study,we demonstrate it using a scene modeling case and provide a preliminary evaluation toward its usability.
