Optimization Of Complex Spatial Join Query Based On WFS Services

With the development of the Internet and geo-spatial information, WFS service-oriented distributed spatial database system has been widely applied to a variety of service industries,such as map query service, the user can according to their own needs for distributed database of multi-way join query processing spatial data sets to get the data they want. However, due to the distributed spatial data sets is more complicated and the amount of the data is huge,making the space connection between different sites query cumbersome and time-consuming,so how to optimize the spatial join query operation has been a hot and difficult study on application of distributed spatial database.The main purpose of the WFS services optimization is to reduce the network data transmission costs by filtering out the non-candidates of spatial data sets before the data transmission between different space sites, thereby reducing the total cost of distributed space database connection query takes. On the basis of the previous studies of a variety of spatial database query methods, this paper studies the complex spatial connection query optimization strategy of WFS services, mainly from the following aspects.Firstly, the basic knowledge of the distributed query optimization is briefly introduced,the WFS service specification and relevant knowledge of XML are described, and the existing problems in the WFS oriented distributed query optimization has been pointed out, as later for the study of WFS service oriented complex spatial join query optimization.Secondly, the space region partition method and semi-join strategy are researched. We compare the quad-tree recursive partitioning method with the KD-tree recursive partitioning method, and analysis the applicable scope of the different methods. We put forward a spatial semi-join region partition strategy for spatial join query optimization, to speed up the efficiency of spatial join query processing.Again, based on the idea of divide and conquer, we put forward a new WFS oriented multi-way spatial join query strategy. This strategy will divide the complex of multi-way spatial join query into a plurality of two way join query, use the filtration rate calculation formula to calculate the filtration rate between space data sets on different sites, through the filtration rate to determine the connection between each two-way connection query sequence,and according to the filtration rate of the discretion to choose whether to adopt space semi-connection area partitioning strategy to optimize the spatial join query, so as to reduce the spatial join query cost.Finally, based on the proposed strategy theory, the simulation experiment is designed to verify the feasibility of the theory. The experiment includes two parts, one is two-way spatial join query experiment based on the different region partition; the other is WFS oriented multi-way spatial join query experiment. We design the algorithm according to the WFS oriented spatial join query strategy, compare and analysis the experimental results between the algorithm and the download data directly algorithm, in order to verify the effective of the WFS oriented spatial join query strategy.The spatial join query optimization strategy proposed can reduce the spatial join query cost better, and improve the efficiency of the spatial join query. It is an effective method for the optimization of WFS oriented complex spatial database system, and it has certain practical value.