Researching And Implementation Of Prefetching Strategy In WebGIS

With rapid development of internet, WebGIS has been an important research areasof space database and geographical information system. With the deeper applicationof WebGIS, amounts of complex data types applied to it have led to unexpected userlatency, making existing prefetching algorithms face various challenges. This thesismainly studies the prefetching algorithm for WebGIS based on Hilbert curve.Firstly, this thesis proposes a prefetching algorithm based on Hilbert curve aimingto address the longer delay introduced by non-spactial data, depending on the analysisand comparisons of characteristics of various data types. It is capable of filteringprefetching objects of low access probability by properly using neighboringrelationship of objects may be accessed. Compared with partition and prefetchingwindow based algorithms, this novel method can improve hit ratio of prefetching, soas to escape from the dilemma traditional prefetching algorithms face, and it canadjust the size of prefetching candidate set according to objects distributed in the mapas well, therefore, it is capable of prefetching complex objects. Analysis andexperiments results show that our approach can reduce the amount of prefetchingcandidates with certain hit ratio under given bandwidth, reduce response timeefficiently and diminish network bandwidth share ratio.This thesis designs a component based multiple layer WebGIS model, andspecifies the designation and implementation depending on J2EE framework, basedon practical pre-research project, aiming at common problems in WebGIS, Thismultiple architecture can improve system performance via adjusting applicationsystems, exploiting middleware to select routing path, and balancing system load.This thesis discusses the implementation and practical applications of NPE basedon above work, then analyzes its performance. The applications show that the NPEsystem with prefetching performs better so that responses more quickly; furthermore,system keeps better integrity and scalability, finally the development term andcomplication can be reduced; meanwhile, the security of the system is assured.In the end, after summarizing the thesis, the work to be improved and possiblefuture researches are pointed out.