面向WFS服务的多路空间连接查询优化理论研究

项目名称： 面向WFS服务的多路空间连接查询优化理论研究

项目编号： No.41261088

项目类型： 地区科学基金项目

立项/批准年度： 2013

项目学科： 天文学、地球科学

项目作者： 蓝贵文

作者单位： 桂林理工大学

项目金额： 48万元

中文摘要： 网络要素服务（WFS）规范支持异构地理信息系统之间矢量空间数据互操作，目前得到多个GIS基础软件平台的支持，应用前景好。在面向WFS服务进行多路空间连接查询时，网络数据传输代价较高且常占主导作用，本项目结合WFS服务规范的特点，借鉴国内外在空间连接处理方面的研究成果，进行以下创新性探讨： （1）提出空间半连接-区域划分的非候选空间对象过滤策略，采用四叉树划分、KD-Tree区域划分方法，降低面向WFS服务的二路空间连接查询网络传输代价。 （2）在几何直方图法和幂指数法的基础上，提出适合于WFS服务规范的格网-几何直方图法和格网-幂指数法，在数据下载之前评估WFS服务的二路空间连接选择率、过滤率。 （3）针对多路空间连接，提出优先执行过滤率高的连接、把重复率高的连接"断开"将查询图分解成为多个子图并行执行等准则，确定各数据集的下载（或连接）次序，从整体上降低网络传输代价。

中文关键词： 空间连接；网络要素服务；查询处理；优化；

英文摘要： The Web Feature Service Implementation Specification has introduced a new way to interoperate spatial data between the heterogeneous geographical information systems. It is regarded as a promising technique as it has been implemented in a lot of well-known GIS softwares. However processing a multi-way-spatial-join query from some WFSs is really a time-consuming task for it usually engages a high transmission cost. Our works are focused on the following aspects: (1)Based on partitioning and spatial semi-jion strategy, a strategy employing quadtree or KD-tree partitioning method is proposed to reduce transmission cost of a 2-way query. (2)The selectivity of the two datasets to be joined is estimated before they are downloaded. Two grid partitioning based techniques, i.e., Geometric histogram and the method of power laws, are modified according to the specification of the WFS. (3) A multi-way spatial join is reduced to the sequences of 2-way joins. We present the following rules to determine the order of the 2-way joins, to ensure the total performance : (1) to run the join with highest filtering rate firstly; (2) the query graph can be broken into several sub-graphs at the joins with high repeation rate and those "broken" joins are run after those sub-graphs that have been concurrently excuted.

英文关键词： Spatial join；Web Feature Service；Query processing；Optimization；